Improved initial and retransmissions of data for v2x transmissions

ABSTRACT

The invention relates to a transmitting device for performing an initial and one or more retransmissions of data via a sidelink interface. A receiver and processor perform a resource sensing procedure to acquire information about radio resources usable for the device to transmit data at a later point in time. The processor performs an autonomous radio resource allocation to select time frequency radio resources within a transmission window to be used for performing a first transmission of the data, based on information acquired by the resource sensing procedure. The processor determines a data transmission timing pattern, that indicates a transmission timing for performing one or more transmissions of data. A transmitter performs the first data transmission using the selected time-frequency radio resources and performs the data retransmissions at the transmission timing defined by the determined data transmission timing pattern with respect to the first data transmission.

BACKGROUND Technical Field

The present disclosure relates to improved data transmissions andresource allocation via the sidelink interface. The present disclosureis providing the corresponding methods and devices for the disclosure.

Description of the Related Art

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving a radioaccess technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. In LTE, scalable multiple transmission bandwidths arespecified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order toachieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM)-based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP) and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA)-based radioaccess was adopted in the uplink, since provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmit power of the user equipment (UE).Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniquesand a highly efficient control signaling structure is achieved in LTERel. 8/9.

LTE Architecture

The overall LTE architecture is shown in FIG. 1. The E-UTRAN consists ofan eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) andcontrol plane (RRC) protocol terminations towards the user equipment(UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control(MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP)layers that include the functionality of user-plane header compressionand encryption. It also offers Radio Resource Control (RRC)functionality corresponding to the control plane. It performs manyfunctions including radio resource management, admission control,scheduling, enforcement of negotiated uplink Quality of Service (QoS),cell information broadcast, ciphering/deciphering of user and controlplane data, and compression/decompression of downlink/uplink user planepacket headers. The eNodeBs are interconnected with each other by meansof the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle-state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g., parameters of the IP bearerservice, or network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle-mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at the time ofintra-LTE handover involving Core Network (CN) node relocation. It isresponsible for authenticating the user (by interacting with the HSS).The Non-Access Stratum (NAS) signaling terminates at the MME, and it isalso responsible for the generation and allocation of temporaryidentities to user equipments. It checks the authorization of the userequipment to camp on the service provider's Public Land Mobile Network(PLMN) and enforces user equipment roaming restrictions. The MME is thetermination point in the network for ciphering/integrity protection forNAS signaling and handles the security key management. Lawfulinterception of signaling is also supported by the MME. The MME alsoprovides the control plane function for mobility between LTE and 2G/3Gaccess networks with the S3 interface terminating at the MME from theSGSN. The MME also terminates the S6a interface towards the home HSS forroaming user equipments.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots as shown in FIG. 2, wherein the firstdownlink slot comprises the control channel region (PDCCH region) withinthe first OFDM symbols. Each subframe consists of a give number of OFDMsymbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release8)), wherein each OFDM symbol spans over the entire bandwidth of thecomponent carrier. The OFDM symbols thus each consist of a number ofmodulation symbols transmitted on respective subcarriers. In LTE, thetransmitted signal in each slot is described by a resource grid ofN_(RB) ^(DL)N_(sc) ^(RB) subcarriers and N_(symb) ^(DL) OFDM symbols.N_(RB) ^(DL) is the number of resource blocks within the bandwidth. Thequantity N_(RB) ^(DL) depends on the downlink transmission bandwidthconfigured in the cell and shall fulfill N_(RB) ^(min,DL)≤N_(RB)^(DL)≤N_(RB) ^(max,DL), where N_(RB) ^(min,DL)=6 and N_(RB)^(max,DL)=110 are respectively the smallest and the largest downlinkbandwidths, supported by the current version of the specification.N_(sc) ^(RB) is the number of subcarriers within one resource block. Fornormal cyclic prefix subframe structure, N_(sc) ^(RB) and N_(symb)^(DL)=7.

Assuming a multi-carrier communication system, e.g., employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource blockAphysical resource block (PRB) is defined as consecutive OFDM symbols inthe time domain (e.g., 7 OFDM symbols) and consecutive subcarriers inthe frequency domain as exemplified in FIG. 2 (e.g., 12 subcarriers fora component carrier). In 3GPP LTE (Release 8), a physical resource blockthus consists of resource elements, corresponding to one slot in thetime domain and 180 kHz in the frequency domain (for further details onthe downlink resource grid, see for example 3GPP TS 36.211, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8)”, current version 13.1.0, section 6.2, availableat http://www.3gpp.org and incorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair”, or equivalent “RB pair” or “PRBpair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources.

Similar assumptions for the component carrier structure will apply tolater releases too.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the StudyItem description on “Further Advancements for E-UTRA (LTE-Advanced)” wasapproved. The study item covers technology components to be consideredfor the evolution of E-UTRA, e.g., to fulfill the requirements onIMT-Advanced.

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers are aggregated inorder to support wider transmission bandwidths up to 100 MHz. Severalcells in the LTE system are aggregated into one wider channel in theLTE-Advanced system which is wide enough for 100 MHz even though thesecells in LTE may be in different frequency bands.

All component carriers can be configured to be LTE Rel. 8/9 compatible,at least when the bandwidth of a component carrier does not exceed thesupported bandwidth of an LTE Rel. 8/9 cell. Not all component carriersaggregated by a user equipment may necessarily be Rel. 8/9 compatible.Existing mechanisms (e.g., barring) may be used to avoid Rel-8/9 userequipments to camp on a component carrier.

A user equipment may simultaneously receive or transmit on one ormultiple component carriers (corresponding to multiple serving cells)depending on its capabilities. An LTE-A Rel. 10 user equipment withreception and/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain (using the 3GPP LTE (Release8/9) numerology).

It is possible to configure a 3GPP LTE-A (Release 10)-compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may currently not be possible toconfigure a mobile terminal with more uplink component carriers thandownlink component carriers. In a typical TDD deployment the number ofcomponent carriers and the bandwidth of each component carrier in uplinkand downlink is the same. Component carriers originating from the sameeNodeB need not provide the same coverage.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time to preserve orthogonality of the subcarrierswith 15 kHz spacing. Depending on the aggregation scenario, the n×300kHz spacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

When carrier aggregation is configured, the mobile terminal only has oneRRC connection with the network. At RRC connectionestablishment/re-establishment, one cell provides the security input(one ECGI, one PCI and one ARFCN) and the non-access stratum mobilityinformation (e.g., TAI) similarly as in LTE Rel. 8/9. After RRCconnection establishment/re-establishment, the component carriercorresponding to that cell is referred to as the downlink Primary Cell(PCell). There is always one and only one downlink PCell (DL PCell) andone uplink PCell (UL PCell) configured per user equipment in connectedstate. Within the configured set of component carriers, other cells arereferred to as Secondary Cells (SCells); with carriers of the SCellbeing the Downlink Secondary Component Carrier (DL SCC) and UplinkSecondary Component Carrier (UL SCC). Maximum five serving cells,including the PCell, can be configured for one UE.

MAC Layer/Entity, RRC Layer, Physical Layer

The LTE layer 2 user-plane/control-plane protocol stack comprises foursublayers, RRC, PDCP, RLC and MAC. The Medium Access Control (MAC) layeris the lowest sublayer in the Layer 2 architecture of the LTE radioprotocol stack and is defined by e.g., the 3GPP technical standard TS36.321, current version 13.2.0. The connection to the physical layerbelow is through transport channels, and the connection to the RLC layerabove is through logical channels. The MAC layer therefore performsmultiplexing and demultiplexing between logical channels and transportchannels: the MAC layer in the transmitting side constructs MAC PDUs,known as transport blocks, from MAC SDUs received through logicalchannels, and the MAC layer in the receiving side recovers MAC SDUs fromMAC PDUs received through transport channels.

The MAC layer provides a data transfer service (see subclauses 5.4 and5.3 of TS 36.321 incorporated herein by reference) for the RLC layerthrough logical channels, which are either control logical channelswhich carry control data (e.g., RRC signaling) or traffic logicalchannels which carry user plane data. On the other hand, the data fromthe MAC layer is exchanged with the physical layer through transportchannels, which are classified as downlink or uplink. Data ismultiplexed into transport channels depending on how it is transmittedover the air.

The Physical layer is responsible for the actual transmission of dataand control information via the air interface, i.e., the Physical Layercarries all information from the MAC transport channels over the airinterface on the transmission side. Some of the important functionsperformed by the Physical layer include coding and modulation, linkadaptation (AMC), power control, cell search (for initialsynchronization and handover purposes) and other measurements (insidethe LTE system and between systems) for the RRC layer. The Physicallayer performs transmissions based on transmission parameters, such asthe modulation scheme, the coding rate (i.e., the modulation and codingscheme, MCS), the number of physical resource blocks etc. Moreinformation on the functioning of the physical layer can be found in the3GPP technical standard 36.213 current version 13.1.1, incorporatedherein by reference.

The Radio Resource Control (RRC) layer controls communication between aUE and an eNB at the radio interface and the mobility of a UE movingacross several cells. The RRC protocol also supports the transfer of NASinformation. For UEs in RRC_IDLE, RRC supports notification from thenetwork of incoming calls. RRC connection control covers all proceduresrelated to the establishment, modification and release of an RRCconnection, including paging, measurement configuration and reporting,radio resource configuration, initial security activation, andestablishment of Signaling Radio Bearer (SRBs) and of radio bearerscarrying user data (Data Radio Bearers, DRBs).

The radio link control (RLC) sublayer comprises mainly ARQ functionalityand supports data segmentation and concatenation, i.e., RLC layerperforms framing of RLC SDUs to put them into the size indicated by theMAC layer. The latter two minimize the protocol overhead independentlyfrom the data rate. The RLC layer is connected to the MAC layer vialogical channels. Each logical channel transports different types oftraffic. The layer above RLC layer is typically the PDCP layer, but insome cases it is the RRC layer, i.e., RRC messages transmitted on thelogical channels BCCH (Broadcast Control Channel), PCCH (Paging ControlChannel) and CCCH (Common Control Channel) do not require securityprotection and thus go directly to the RLC layer, bypassing the PDCPlayer.

Uplink Access Scheme for LTE

For uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and improved coverage(higher data rates for a given terminal peak power). During each timeinterval, eNodeB assigns users a unique time/frequency resource fortransmitting user data, thereby ensuring intra-cell orthogonality. Anorthogonal access in the uplink promises increased spectral efficiencyby eliminating intra-cell interference. Interference due to multipathpropagation is handled at the base station (eNodeB), aided by insertionof a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BWgrant during one time interval, e.g., asubframe, onto which coded information bits are mapped. It should benoted that a subframe, also referred to as transmission time interval(TTI), is the smallest time interval for user data transmission. It ishowever possible to assign a frequency resource BWgrant over a longertime period than one TTI to a user by concatenation of subframes.

Layer 1/Layer 2 Control Signaling

In order to inform the scheduled users about their allocation status,transport format, and other transmission-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length can be amultiple of the subframes. The TTI length may be fixed in a service areafor all users, may be different for different users, or may even bydynamic for each user. Generally, the L1/2 control signaling needs onlybe transmitted once per TTI. Without loss of generality, the followingassumes that a TTI is equivalent to one subframe.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which in most cases includes resource assignments andother control information for a mobile terminal or groups of UEs.Several PDCCHs can be transmitted in one subframe.

Generally, the information sent in the L1/L2 control signaling forassigning uplink or downlink radio resources (particularly LTE(-A)Release 10) can be categorized to the following items:

User identity, indicating the user that is allocated. This is typicallyincluded in the checksum by masking the CRC with the user identity;

Resource allocation information, indicating the resources (e.g.,Resource Blocks, RBs) on which a user is allocated. Alternatively, thisinformation is termed resource block assignment (RBA). Note, that thenumber of RBs on which a user is allocated can be dynamic;

Carrier indicator, which is used if a control channel transmitted on afirst carrier assigns resources that concern a second carrier, i.e.,resources on a second carrier or resources related to a second carrier;(cross carrier scheduling);

Modulation and coding scheme that determines the employed modulationscheme and coding rate;

HARQ information, such as a new data indicator (NDI) and/or a redundancyversion (RV) that is particularly useful in retransmissions of datapackets or parts thereof;

Power control commands to adjust the transmit power of the assigneduplink data or control information transmission;

Reference signal information such as the applied cyclic shift and/ororthogonal cover code index, which are to be employed for transmissionor reception of reference signals related to the assignment;

Uplink or downlink assignment index that is used to identify an order ofassignments, which is particularly useful in TDD systems;

Hopping information, e.g., an indication whether and how to applyresource hopping in order to increase the frequency diversity;

CSI request, which is used to trigger the transmission of channel stateinformation in an assigned resource; and

Multi-cluster information, which is a flag used to indicate and controlwhether the transmission occurs in a single cluster (contiguous set ofRBs) or in multiple clusters (at least two non-contiguous sets ofcontiguous RBs). Multi-cluster allocation has been introduced by 3GPPLTE-(A) Release 10.

It is to be noted that the above listing is non-exhaustive, and not allmentioned information items need to be present in each PDCCHtransmission depending on the DCI format that is used.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in their fields asmentioned above. The different DCI formats that are currently definedfor LTE are as follows and described in detail in 3GPP TS 36.212,“Multiplexing and channel coding”, section 5.3.3.1 (current versionv13.1.0 available at http://www.3gpp.org and incorporated herein byreference). The 3GPP technical standard TS 36.212, current version13.1.0, defines in subclause 5.4.3, incorporated herein by reference,control information for the sidelink interface.

Semi-Persistent Scheduling (SPS)

In the downlink and uplink, the scheduling eNodeB dynamically allocatesresources to user equipments at each transmission time interval via theL1/L2 control channel(s) (PDCCH) where the user equipments are addressedvia their specific C-RNTIs. As already mentioned before, the CRC of aPDCCH is masked with the addressed user equipment's C-RNTI (so-calleddynamic PDCCH). Only a user equipment with a matching C-RNTI can decodethe PDCCH content correctly, i.e., the CRC check is positive. This kindof PDCCH signaling is also referred to as dynamic (scheduling) grant. Auser equipment monitors at each transmission time interval the L1/L2control channel(s) for a dynamic grant in order to find a possibleallocation (downlink and uplink) it is assigned to.

In addition, E-UTRAN can allocate uplink/downlink resources for initialHARQ transmissions persistently. When required, retransmissions areexplicitly signaled via the L1/L2 control channel(s). Sinceretransmissions are dynamically scheduled, this kind of operation isreferred to as semi-persistent scheduling (SPS), i.e., resources areallocated to the user equipment on a semi-persistent basis(semi-persistent resource allocation). The benefit is that PDCCHresources for initial HARQ transmissions are saved. Semi-persistentscheduling may be used in the PCell in Release 10, but not in an SCell.

One example for a service, which might be scheduled usingsemi-persistent scheduling, is Voice over IP (VoIP). Every 20 ms a VoIPpacket is generated at the codec during a talk-spurt. Therefore, eNodeBcould allocate uplink or respectively downlink resources persistentlyevery 20 ms, which could be then used for the transmission of Voice overIP packets. In general, semi-persistent scheduling is beneficial forservices with a predictable traffic behavior, i.e., constant bit rate,packet arrival time is periodic.

The user equipment also monitors the PDCCHs in a subframe where it hasbeen allocated resources for an initial transmission persistently. Adynamic (scheduling) grant, i.e., PDCCH with a C-RNTI-masked CRC, canoverride a semi-persistent resource allocation. In case the userequipment finds its C-RNTI on the L1/L2 control channel(s) in thesub-frames where the user equipment has a semi-persistent resourceassigned, this L1/L2 control channel allocation overrides the persistentresource allocation for that transmission time interval, and the userequipment does follow the dynamic grant. When a user equipment does notfind a dynamic grant, it will transmit/receive according to thesemi-persistent resource allocation.

The configuration of semi-persistent scheduling is done by RRCsignaling. For example the periodicity, e.g., PS_PERIOD, of thepersistent allocation is signaled within Radio resource Control (RRC)signaling. The activation of a persistent allocation and also the exacttiming as well as the physical resources and transport format parametersare sent via PDCCH signaling. Once semi-persistent scheduling isactivated, the user equipment follows the semi-persistent resourceallocation according to the SPS activation PDCCH every PS_PERIOD.Essentially, the user equipment stores the SPS activation PDCCH contentand follows the PDCCH with the signaled periodicity.

In order to distinguish a dynamic PDCCH from a PDCCH which activatessemi-persistent scheduling (also referred to as SPS activation PDCCH), aseparate identity is introduced. Basically, the CRC of an SPS activationPDCCH is masked with this additional identity which is in the followingreferred to as SPS C-RNTI. The size of the SPS C-RNTI is also 16 bits,same as the normal C-RNTI. Furthermore, the SPS C-RNTI is also userequipment-specific, i.e., each user equipment configured forsemi-persistent scheduling is allocated a unique SPS C-RNTI.

In case a user equipment detects that a semi-persistent resourceallocation is activated by a corresponding SPS activation PDCCH, theuser equipment will store the PDCCH content (i.e., the semi-persistentresource assignment) and apply it every semi-persistent schedulinginterval, i.e., periodicity signaled via RRC. As already mentioned, adynamic allocation, i.e., signaled on dynamic PDCCH, is only a “one-timeallocation”. Retransmissions of an SPS allocation are also signaledusing the SPS C-RNTI. In order to distinguish the SPS activation from anSPS re-transmission, the NDI (new data indicator) bit is used. An SPSactivation is indicated by setting the NDI bit to 0. An SPS PDCCH withthe NDI-bit set to 1 indicates a re-transmission for a semi-persistentlyscheduled initial transmission.

Similar to the activation of semi-persistent scheduling, the eNodeB alsocan deactivate semi-persistent scheduling, also called SPS resourcerelease. There are several options how a semi-persistent schedulingde-allocation can be signaled. One option would be to use PDCCHsignaling with some PDCCH fields set to some predefined values, i.e.,SPS PDCCH indicating a zero size resource allocation. Another optionwould be to use MAC control signaling.

LTE Device to Device (D2D) Proximity Services (ProSe)

Proximity-based applications and services represent an emergingsocial-technological trend. The identified areas include servicesrelated to commercial services and Public Safety that would be ofinterest to operators and users. The introduction of a ProximityServices (ProSe) capability in LTE allows the 3GPP industry to servethis developing market and will, at the same time, serve the urgentneeds of several Public Safety communities that are jointly committed toLTE.

Device-to-Device (D2D) communication is a technology componentintroduced by LTE-Rel.12, which allows D2D as an underlay to thecellular network to increase the spectral efficiency. For example, ifthe cellular network is LTE, all data-carrying physical channels useSC-FDMA for D2D signaling. In D2D communications, user equipmentstransmit data signals to each other over a direct link using thecellular resources instead of through the radio base station. Throughoutthe disclosure the terms “D2D”, “ProSe” and “sidelink” areinterchangeable.

The D2D communication in LTE is focusing on two areas: Discovery andCommunication.

ProSe (Proximity-based Services) Direct Discovery is defined as theprocedure used by the ProSe-enabled UE to discover other ProSe-enabledUE(s) in its proximity using E-UTRA direct radio signals via the PC5interface.

In D2D communication, UEs transmit data signals to each other over adirect link using the cellular resources instead of through the basestation (BS). D2D users communicate directly while remaining controlledunder the BS, i.e., at least when being in coverage of an eNB.Therefore, D2D can improve system performance by reusing cellularresources.

It is assumed that D2D operates in the uplink LTE spectrum (in the caseof FDD) or uplink sub-frames of the cell giving coverage (in case ofTDD, except when out of coverage). Furthermore, D2Dtransmission/reception does not use full duplex on a given carrier. Fromindividual UE perspective, on a given carrier D2D signal reception andLTE uplink transmission do not use full duplex, i.e., no simultaneousD2D signal reception and LTE UL transmission is possible.

In D2D communication, when one particular UE1 has a role of transmission(transmitting user equipment or transmitting terminal), UE1 sends data,and another UE2 (receiving user equipment) receives it. UE1 and UE2 canchange their transmission and reception role. The transmission from UE1can be received by one or more UEs like UE2.

ProSe Direct Communication Layer-2 Link

In brief, ProSe direct one-to-one communication is realized byestablishing a secure layer-2 link over PC5 between two UEs. Each UE hasa Layer-2 ID for unicast communication that is included in the SourceLayer-2 ID field of every frame that it sends on the layer-2 link and inthe Destination Layer-2 ID of every frame that it receives on thelayer-2 link. The UE needs to ensure that the Layer-2 ID for unicastcommunication is at least locally unique. So the UE should be preparedto handle Layer-2 ID conflicts with adjacent UEs using unspecifiedmechanisms (e.g., self-assign a new Layer-2 ID for unicast communicationwhen a conflict is detected). The layer-2 link for ProSe directcommunication one-to-one is identified by the combination of the Layer-2IDs of the two UEs. This means that the UE can engage in multiplelayer-2 links for ProSe direct communication one-to-one using the sameLayer-2 ID.

ProSe direct communication one-to-one is composed of the followingprocedures as explained in detail in TR 23.713 current version v13.0.0section 7.1.2 incorporated herein by reference:

-   -   Establishment of a secure layer-2 link over PC5.    -   IP address/prefix assignment.    -   Layer-2 link maintenance over PC5.    -   Layer-2 link release over PC5.

FIG. 3 illustrates how to establish a secure layer-2 link over the PC5interface.

1. UE-1 sends a Direct Communication Request message to UE-2 in order totrigger mutual authentication. The link initiator (UE-1) needs to knowthe Layer-2 ID of the peer (UE-2) in order to perform step 1. As anexample, the link initiator may learn the Layer-2 ID of the peer byexecuting a discovery procedure first or by having participated in ProSeone-to-many communication including the peer.

2. UE-2 initiates the procedure for mutual authentication. Thesuccessful completion of the authentication procedure completes theestablishment of the secure layer-2 link over PC5.

UEs engaging in isolated (non-relay) one-to-one communication may alsouse link-local addresses. The PC5 Signaling Protocol shall supportkeep-alive functionality that is used to detect when the UEs are not inProSe Communication range, so that they can proceed with implicitlayer-2 link release. The Layer-2 link release over the PC5 can beperformed by using a Disconnect Request message transmitted to the otherUE, which also deletes all associated context data. Upon reception ofthe Disconnect Request message, the other UE responds with a DisconnectResponse message and deletes all context data associated with thelayer-2 link.

ProSe Direct Communication Related Identities

3GPP TS 36.300, current version 13.3.0, defines in subclause 8.3 thefollowing identities to use for ProSe Direct Communication:

-   -   SL-RNTI: Unique identification used for ProSe Direct        Communication Scheduling;    -   Source Layer-2 ID: Identifies the sender of the data in sidelink        ProSe Direct Communication. The Source Layer-2 ID is 24 bits        long and is used together with ProSe Layer-2 Destination ID and        LCD for identification of the RLC UM entity and PDCP entity in        the receiver;    -   Destination Layer-2 ID: Identifies the target of the data in        sidelink ProSe Direct Communication. The Destination Layer-2 ID        is 24 bits long and is split in the MAC layer into two bit        strings:    -   One bit string is the LSB part (8 bits) of Destination Layer-2        ID and forwarded to the physical layer as Sidelink Control        Layer-1 ID. This identifies the target of the intended data in        Sidelink Control and is used for filtering packets at the        physical layer.    -   Second bit string is the MSB part (16 bits) of the Destination        Layer-2 ID and is carried within the MAC header. This is used        for filtering packets at the MAC layer.

No Access Stratum signaling is required for group formation and toconfigure Source Layer-2 ID, Destination Layer-2 ID and Sidelink ControlL1 ID in the UE. These identities are either provided by a higher layeror derived from identities provided by a higher layer. In case ofgroupcast and broadcast, the ProSe UE ID provided by the higher layer isused directly as the Source Layer-2 ID, and the ProSe Layer-2 Group IDprovided by the higher layer is used directly as the Destination Layer-2ID in the MAC layer. In case of one-to-one communications, higher layerprovides Source Layer-2 ID and Destination Layer-2 ID.

Radio Resource Allocation for Proximity Services

From the perspective of a transmitting UE, a Proximity-Services-enabledUE (ProSe-enabled UE) can operate in two modes for resource allocation:

Mode 1 refers to the eNB-scheduled resource allocation mode, where theUE requests transmission resources from the eNB (or Release-10 relaynode), and the eNodeB (or Release-10 relay node) in turn schedules theresources used by a UE to transmit direct data and direct controlinformation (e.g., Scheduling Assignment). The UE needs to beRRC_CONNECTED in order to transmit data. In particular, the UE sends ascheduling request (D-SR or Random Access) to the eNB followed by asidelink buffer status report (BSR) in the usual manner (see alsofollowing chapter “Transmission procedure for D2D communication”). Basedon the BSR, the eNB can determine that the UE has data for a ProSeDirect Communication transmission and can estimate the resources neededfor transmission.

On the other hand, Mode 2 refers to the UE-autonomous resource selectionmode, where a UE on its own selects resources (time and frequency) fromresource pool(s) to transmit direct data and direct control information(i.e., SA). At least one resource pool is defined e.g., by the contentof SIB18, namely by the field commTxPoolNormalCommon, these particularresource pool(s) being broadcast in the cell and then commonly availablefor all UEs in the cell still in RRC_Idle state. Effectively, the eNBmay define up to four different instances of said pool, respectivelyfour resource pools for the transmission of SA messages and direct data.However, in Rel-12 a UE shall always use the first resource pool definedin the list, even if it was configured with multiple resource pools.This restriction was removed for Rel-13, i.e., a UE can transmit onmultiple of the configured resource pools within one SC period. How theUE selects the resource pools for transmission is further outlined below(further specified in TS36.321).

As an alternative, another resource pool can be defined by the eNB andsignaled in SIB18, namely by using the field commTxPoolExceptional,which can be used by the UEs in exceptional cases.

What resource allocation mode a UE is going to use is configurable bythe eNB. Furthermore, what resource allocation mode a UE is going to usefor D2D data communication may also depend on the RRC state, i.e.,RRC_IDLE or RRC_CONNECTED, and the coverage state of the UE, i.e.,in-coverage, out-of-coverage. A UE is considered in-coverage if it has aserving cell (i.e., the UE is RRC_CONNECTED or is camping on a cell inRRC_IDLE).

FIG. 4 illustrates the use of transmission/reception resources foroverlay (LTE) and underlay (D2D) system.

Basically, the eNodeB controls whether UE may apply the Mode 1 or Mode 2transmission. Once the UE knows its resources where it can transmit (orreceive) D2D communication, it uses the corresponding resources only forthe corresponding transmission/reception. For example, in FIG. 4 the D2Dsubframes will only be used to receive or transmit the D2D signals.Since the UE as a D2D device would operate in Half Duplex mode, it caneither receive or transmit the D2D signals at any point of time.Similarly, the other subframes illustrated in FIG. 4 can be used for LTE(overlay) transmissions and/or reception.

Transmission Procedure for D2D Communication

The D2D data transmission procedure according to Rel. 12/13 differsdepending on the resource allocation mode. As described above for Mode1, the eNB explicitly schedules the resources for the SchedulingAssignment and the D2D data communication after a corresponding requestfrom the UE. Particularly, the UE may be informed by the eNB that D2Dcommunication is generally allowed, but that no Mode 2 resources (i.e.,resource pool) are provided; this may be done e.g., with the exchange ofthe D2D communication Interest Indication by the UE and thecorresponding response, D2D Communication Response, where thecorresponding exemplary ProseCommConfig information element would notinclude the commTxPoolNormalCommon, meaning that a UE that wants tostart direct communication involving transmissions has to requestE-UTRAN to assign resources for each individual transmission. Thus, insuch a case, the UE has to request the resources for each individualtransmission, and in the following the different steps of therequest/grant procedure are exemplarily listed for this Mode 1 resourceallocation:

-   -   Step 1: UE sends SR (Scheduling Request) to eNB via PUCCH;    -   Step 2: eNB grants UL resource (for UE to send sidelink BSR) via        PDCCH, scrambled by C-RNTI;    -   Step 3: UE sends D2D/sidelink BSR indicating the buffer status        via PUSCH;    -   Step 4: eNB grants D2D resource (for UE to send data) via PDCCH,        scrambled by D2D-RNTI.    -   Step 5: D2D Tx UE transmits SA/D2D data according to grant        received in step 4.

A Scheduling Assignment (SA), also termed SCI (Sidelink ControlInformation) is a compact (low-payload) message containing controlinformation, e.g., pointer(s) to time-frequency resources, modulationand coding scheme and Group Destination ID for the corresponding D2Ddata transmission. An SCI transports the sidelink scheduling informationfor one (ProSe) destination ID. The content of the SA (SCI) is basicallyin accordance with the grant received in Step 4 above. The D2D grant andSA content (i.e., SCI content) are defined in the 3GPP technicalstandard 36.212, current version 13.1.0, subclause 5.4.3, incorporatedherein by reference, defining in particular the SCI format 0 (seecontent of SCI format 0 above).

On the other hand, for Mode 2 resource allocation, above steps 1-4 arebasically not necessary, and the UE autonomously selects radio resourcesfor the SA and D2D data transmission from the transmission resourcepool(s) configured and provided by the eNB.

FIG. 5 exemplarily illustrates the transmission of the SchedulingAssignment and the D2D data for two UEs, UE-1 and UE-2, where theresources for sending the scheduling assignments are periodic, and theresources used for the D2D data transmission are indicated by thecorresponding Scheduling Assignment.

FIG. 6 illustrates one specific example of the D2D communication timingfor Mode 2, autonomous scheduling, during one SA/data period, also knownas SC period, Sidelink Control period. FIG. 7 illustrates the D2Dcommunication timing for Mode 1, eNB-scheduled allocation during oneSA/data period. In Rel. 13, 3GPP defined an SC period as being the timeperiod consisting of transmission of a Scheduling Assignment and itscorresponding data. As can be seen from FIG. 6, the UE transmits afteran SA-offset time, a Scheduling Assignment using the transmission poolresources for scheduling assignments for Mode 2, SA_Mode2_Txpool. The1st transmission of the SA is followed e.g., by three retransmissions ofthe same SA message. Then, the UE starts the D2D data transmission,i.e., more in particular the T-RPT bitmap/pattern, at some configuredoffset (Mode2data_offset) after the first subframe of the SA resourcepool (given by the SA_offset). One D2D data transmission of a MAC PDU(i.e., a transport block) consists of its 1st initial transmission andseveral retransmissions. For the illustration of FIG. 6 (and of FIG. 7)it is assumed that three retransmissions are performed (i.e., 2nd, 3rd,and 4th transmission of the same MAC PDU). The Mode2 T-RPT Bitmap (timeresource pattern of transmission, T-RPT) basically defines the timing ofthe MAC PDU transmission (1st transmission) and its retransmissions(2^(nd), 3^(rd), and 4^(th) transmission). The SA pattern basicallydefines the timing of the SA's initial transmission and itsretransmissions (2nd 3rd and 4^(th) transmission). More information onthe T-RPT can be found in the 3GPP technical standard 36.213 v.13.1.1,particularly in section 14 “UE procedures related to the Sidelink”,incorporated herein by reference.

As currently specified in the standard, for one sidelink grant, e.g.,either sent by the eNB or selected by the UE itself, the UE can transmitmultiple transport blocks, MAC PDUs, (only one per subframe (TTI), i.e.,one after the other), however to only one ProSe destination group. Alsothe retransmissions of one transport block must be finished before thefirst transmission of the next transport block starts, i.e., only oneHARQ process is used per sidelink grant for the transmission of themultiple transport blocks. Furthermore, the UE can have and use severalsidelink grants per SC period, but a different ProSe destination beselected for each of them. Thus, in one SC period the UE can transmitdata to one ProSe destination only one time.

As apparent from FIG. 7, for the eNB-scheduled resource allocation mode(Mode 1), the D2D data transmission, i.e., more in particular the T-RPTpattern/bitmap, starts in the next UL subframe after the last SAtransmission repetition in the SA resource pool. As explained alreadyfor FIG. 6, the Mode1 T-RPT Bitmap (time resource pattern oftransmission, T-RPT) basically defines the timing of the MAC PDUtransmission (1st transmission) and its retransmissions (2nd, 3rd, and4th transmission).

The sidelink data transmission procedure can be found in the 3GPPstandard document TS 36.321 v13.2.0, section 5.14, incorporated hereinby reference. Therein, the Mode-2 autonomous resource selection isdescribed in detail, differentiating between being configured with asingle radio resource pool or multiple radio resource pools.

What is discussed above is the current status of the 3GPP standard forthe D2D communication. However, it should be noted that there has beenongoing discussions on how to further improve and enhance the D2Dcommunication which will likely result in that some changes areintroduced to the D2D communication in future releases. The presentdisclosure as will be described later shall be also applicable to thoselater releases.

For example, for 3GPP Rel. 14 which is currently under development, 3GPPmay decide to change the transmission timing so as to no longer be basedon SC periods as discussed above, but differently (e.g., based onsubframes same/similar to Uu interface transmissions). Correspondingly,the above detailed examples on how transmissions over the sidelink (PC5)interface can be performed are merely exemplary and may apply to Rel.13, but possibly not for later releases of the corresponding 3GPPstandards.

Furthermore, in future releases of the D2D framework, particularly inconnection with vehicular communication, transmissions based on fixedT-RPTs might not be used anymore.

ProSe Network Architecture and ProSe Entities

FIG. 8 illustrates a high-level exemplary architecture for a non-roamingcase, including different ProSe applications in the respective UEs A andB, as well as a ProSe Application Server and ProSe function in thenetwork. The example architecture of FIG. 8 is taken from TS 23.303v.13.2.0 chapter 4.2 “Architectural Reference Model” incorporated hereinby reference.

The functional entities are presented and explained in detail in TS23.303 subclause 4.4 “Functional Entities” incorporated herein byreference. The ProSe function is the logical function that is used fornetwork-related actions required for ProSe and plays different roles foreach of the features of ProSe. The ProSe function is part of the 3GPP'sEPC and provides all relevant network services like authorization,authentication, data handling etc. related to proximity services. ForProSe direct discovery and communication, the UE may obtain a specificProSe UE identity, other configuration information, as well asauthorization from the ProSe function over the PC3 reference point.There can be multiple ProSe functions deployed in the network, althoughfor ease of illustration a single ProSe function is presented. The ProSefunction consists of three main sub-functions that perform differentroles depending on the ProSe feature: Direct Provision Function (DPF),Direct Discovery Name Management Function, and EPC-level DiscoveryFunction. The DPF is used to provision the UE with the necessaryparameters to use ProSe Direct Discovery and ProSe Direct Communication.

The term “UE” used in said connection refers to a ProSe-enabled UEsupporting ProSe functionality, such as:

-   -   Exchange of ProSe control information between ProSe-enabled UE        and the ProSe Function over PC3 reference point.    -   Procedures for open ProSe Direct Discovery of other        ProSe-enabled UEs over PC5 reference point.    -   Procedures for one-to-many ProSe Direct Communication over PC5        reference point.    -   Procedures to act as a ProSe UE-to-Network Relay. The Remote UE        communicates with the ProSe UE-to-Network Relay over PC5        reference point. The ProSe UE-to Network Relay uses layer-3        packet forwarding.    -   Exchange of control information between ProSe UEs over PC5        reference point, e.g., for UE-to-Network Relay detection and        ProSe Direct Discovery.    -   Exchange of ProSe control information between another        ProSe-enabled UE and the ProSe Function over PC3 reference        point. In the ProSe UE-to-Network Relay case the Remote UE will        send this control information over PC5 user plane to be relayed        over the LTE-Uu interface towards the ProSe Function.    -   Configuration of parameters (e.g., including IP addresses, ProSe        Layer-2 Group IDs, Group security material, radio resource        parameters). These parameters can be pre-configured in the UE,        or, if in coverage, provisioned by signaling over the PC3        reference point to the ProSe Function in the network.

The ProSe Application Server supports the Storage of EPC ProSe User IDs,and ProSe Function IDs, and the mapping of Application Layer User IDsand EPC ProSe User IDs. The ProSe Application Server (AS) is an entityoutside the scope of 3GPP. The ProSe application in the UE communicateswith the ProSe AS via the application-layer reference point PC1. TheProSe AS is connected to the 3GPP network via the PC2 reference point.

Vehicular Communication—V2X Services

A new study item has been set up in the 3GPP in Rel. 14 to consider theusefulness of new LTE features to the automotive industry—includingProximity Service (ProSe) and LTE-based broadcast services. The ProSefunctionality explained above is thus considered as offering a goodfoundation for the V2X services. Changes to the D2D framework arediscussed with regard to how the transmission of vehicular communicationcan be enhanced. For instance, T-RPT patterns might not be used anymore. Furthermore, instead of or in addition to using TDD as discussedbefore for the transmission of data and SA, frequency divisionmultiplexing may be foreseen. Cooperative services in vehicularscenarios are becoming essential for future connected vehicles withinthe ITS (Intelligent Transportation Systems) research field. They aresupposed to decrease road fatalities, improve the capacity of roads,diminish the carbon footprint of road transport and enhance the userexperience during travels.

V2X communication is the passing of information from a vehicle to anyentity that may affect the vehicle, and vice versa. This informationexchange can be used to improve safety, mobility and environmentalapplications to include driver assistance vehicle safety, speedadaptation and warning, emergency response, travel information,navigation, traffic operations, commercial fleet planning and paymenttransactions.

LTE support for V2X services contains 3 types of different use caseswhich are the following:

-   -   V2V: covering LTE-based communication between vehicles.    -   V2P: covering LTE-based communication between a vehicle and a        device carried by an individual (e.g., handheld terminal carried        by a pedestrian, cyclist, driver or passenger).    -   V2I: covering LTE-based communication between a vehicle and a        road side unit.

These three types of V2X can use “co-operative awareness” to providemore intelligent services for end-users. This means that transportentities, such as vehicles, roadside infrastructure, and pedestrians,can collect knowledge of their local environment (e.g., informationreceived from other vehicles or sensor equipment in proximity) toprocess and share that knowledge in order to provide more intelligentservices, such as cooperative collision warning or autonomous driving.

With regard to V2V communication, E-UTRAN allows such (vehicle) UEs thatare in proximity of each other to exchange V2V-related information usingE-UTRA(N) when permission, authorization and proximity criteria arefulfilled. The proximity criteria can be configured by the MNO (MobileNetwork Operator). However, UEs supporting V2V Service can exchange suchinformation when served by or not served by E-UTRAN which supports V2XService.

The device (vehicle UE) supporting V2V applications transmitsapplication layer information (e.g., about its location, dynamics, andattributes as part of the V2V Service). The V2V payload must be flexiblein order to accommodate different information contents, and theinformation can be transmitted periodically according to a configurationprovided by the MNO.

V2V is predominantly broadcast-based; V2V includes the exchange ofV2V-related application information between distinct devices directlyand/or, due to the limited direct communication range of V2V, theexchange of V2V-related application information between distinct devicesvia infrastructure supporting V2X Service, e.g., RSU, applicationserver, etc.

With regard to V2I communication, the device supporting V2I applicationssends application layer information to the Road Side Unit, which in turncan send application layer information to a group of devices or a devicesupporting V2I applications.

V2N (Vehicle to Network, eNB/CN) is also introduced where one party is aUE and the other party is a serving entity, both supporting V2Napplications and communicating with each other via LTE network.

With regard to V2P communication, E-UTRAN allows such UEs that are inproximity of each other to exchange V2P-related information usingE-UTRAN when permission, authorization and proximity criteria arefulfilled. The proximity criteria can be configured by the MNO. However,UEs supporting V2P Service can exchange such information even when notserved by E-UTRAN which supports V2X Service.

The UE supporting V2P applications transmits application layerinformation. Such information can be broadcast by a vehicle with UEsupporting V2X Service (e.g., warning to pedestrian), and/or by apedestrian with UE supporting V2X Service (e.g., warning to vehicle).

V2P includes the exchange of V2P-related application information betweendistinct UEs (one for vehicle and the other for pedestrian) directlyand/or, due to the limited direct communication range of V2P, theexchange of V2P-related application information between distinct UEs viainfrastructure supporting V2X Service, e.g., RSU, application server,etc.

For this new study item V2X, 3GPP has provided particular terms anddefinition in TR 21.905, current version 13.0.0, which can be reused forthis application.

Road Side Unit (RSU): An entity supporting V2I Service that can transmitto, and receive from a UE using V2I application. An RSU can beimplemented in an eNB or a stationary UE.

V2I Service: A type of V2X Service, where one party is a UE and theother party is an RSU both using V2I application.

V2N Service: A type of V2X Service, where one party is a UE and theother party is a serving entity, both using V2N applications andcommunicating with each other via LTE network entities.

V2P Service: A type of V2X Service, where both parties of thecommunication are UEs using V2P application.

V2V Service: A type of V2X Service, where both parties of thecommunication are UEs using V2V application.

V2X Service: A type of communication service that involves atransmitting or receiving UE using V2V application via 3GPP transport.Based on the other party involved in the communication, it can befurther divided into V2V Service, V2I Service, V2P Service, and V2NService.

Many ITS services have common communication requirements:

-   -   Periodic status exchange. ITS services typically need to know        about the status of vehicle or roadside terminals. This implies        the periodic exchange of data packets with information about        location, speed, identifier, etc.    -   Asynchronous notifications. This kind of messages is used to        inform about a specific service event. In contrast to the        previous status messages, the reliable delivery of these        messages to a single terminal or a group of them is usually a        key requirement.

Examples of the usage of the first communication type can be found ontraffic efficiency services such as remote vehicle monitoring, whichgathers periodic status data from vehicles, or safety services such ascooperative collision avoidance, which requires kinematic informationabout surrounding vehicles to detect potential impacts. Asynchronousnotifications are mainly found in safety services, such as slipperypavement or post-collision warning.

Different types of messages are and will be defined for the V2Vcommunication. Two different types of messages have been already definedby ETSI for the Intelligent Transport Systems (ITS), see correspondingEuropean Standards ETSI EN 302 637-2 v1.3.1 and ETSI EN 302 637-3v1.2.1:

-   -   Cooperative Awareness Messages (CAM), which are continuously        triggered by vehicle dynamics to reflect the vehicle status.    -   Decentralized Environmental Notification Messages (DENM), which        are triggered only when vehicle-related safety events occur.

As the V2V and ITS standardizations are rather at the beginning, it isto be expected that other messages might be defined in the future.

CAMs are continuously (periodically) broadcast by ITS-Stations (ITS-S)to exchange status information with other ITS-Ss, and thus have a largerimpact on the traffic load than event-triggered (aperiodic) DENMmessages. Essentially CAM messages are a kind of heartbeat messagesperiodically broadcasted by each vehicle to its neighbors to provideinformation of presence, position, temperature, and basic status. On thecontrary, DENMs are event-triggered messages broadcasted to alert roadusers of a hazardous event. For this reason, traffic characteristics ofCAM messages as defined by ETSI for ITS are considered morerepresentative of V2V traffic.

Cooperative Awareness Messages (CAMs) are messages exchanged in the ITSnetwork between ITS-Ss to create and maintain awareness of each otherand to support cooperative performance of vehicles using the roadnetwork. Point to multipoint communication shall be used fortransmitting CAMs, such that the CAMs are transmitted from theoriginating ITS-S to the receiving ITS-Ss located in the directcommunication range of the originating ITS-S. CAM generation shall betriggered and managed by the Cooperative Awareness basic service, whichdefines the time interval between two consecutive CAM generations. Atpresent, the upper and lower limits of the transmission interval are 100ms (i.e., CAM generation rate of 10 Hz) and 1000 ms (i.e., CAMgeneration rate of 1 Hz). The underlying philosophy of ETSI ITS is tosend CAMs when there is new information to share (e.g., new position,new acceleration or new heading values). Correspondingly, when thevehicles are moving slowly and on constant heading and speed, a high CAMgeneration rate brings no real benefit because the CAMs only displayminimal differences. The transmission frequency of CAMs of one vehiclevaries between 1 HZ to 10 Hz as a function of the vehicle dynamics(e.g., speed, acceleration, and heading). For instance, the slower thevehicle drives, the less number of CAMs are triggered and transmitted.Vehicle speed is the main impacting factor on CAM traffic generation.

In the above, the periodic Cooperative Awareness messages have beendescribed. However, it should be noted that although some of the aboveinformation has already been standardized, other information, such asthe periodicities and the message sizes, are not standardized yet andare based on assumptions. Furthermore, the standardization might changein the future and thus might also change aspects of how the CAMs aregenerated and transmitted.

In order for the vehicular UE to have radio resources on the sidelink totransmit the CAMs, Mode1 and/or Mode2 radio resource allocation areenvisioned as explained above. For Mode 1 radio resource allocation, theeNB allocates resources for the SA message and data for each SA period.However, when there is a lot of traffic (e.g., high-frequency periodictraffic), the overhead on the Uu link from UE to the eNB could be big.

As apparent from the above, a lot of V2V traffic is periodical, suchthat the 3GPP has agreed that for sidelink V2V communication Mode 1(i.e., eNB scheduled radio resource allocation), sidelinksemi-persistent radio resource allocation will be supported by eNBs andUEs.

It was agreed to support a sensing mechanism together withsemi-persistent transmissions for assisting the autonomous resourcecontrol/selection mechanism for the V2X sidelink. The UE would indicatewithin the PSCCH (SA/SCI) that it has data on a selected set ofperiodically occurring resources until a resource selection occurs. Thisresource reservation information (signaled within the SCI) can be usedby other UEs which are intending to transmit a V2X message for theselection of a resource such that resources that are alreadyreserved/booked by other UEs are not considered for radio resourceselection. This resource reservation/booking procedure is particularlysuitable for traffic for which packets arrive with a certainperiodicity, e.g., CAM messages.

The indication of reserved radio resources in the scheduling informationas mentioned above can be monitored (“sensed”) by other (vehicular)devices. In general, the sensing procedure collects information on radioresources and thus allows predictions on future radio resources whichcan be used in the resource allocation procedure to identify a set ofresource candidates for transmission. Very few things have been alreadyagreed by 3GPP, but it may be assumed that the sensing processcategorizes time frequency resources into:

-   -   ‘Unavailable’ resources. These are the resources on which the UE        is not allowed to transmit since those resources are already        booked/reserved by other UEs, and    -   ‘candidate (or available) resources’. These are the resources on        which the UE may/can perform a transmission.

Furthermore, 3GPP agreed to also perform energy measurement for thesensing procedure, although the agreement did not provide for anydetails about how and what energy measurements are to be performed.Energy-based sensing can be understood as a process where UE measuresreceived signal strength on PSSCH radio resources and/or PSCCH radioresources. Energy-based sensing essentially may be helpful to identifynear versus far interferers.

Furthermore, it was discussed whether the priority of the data (orcorresponding radio resource reservation) is indicated in the schedulingassignment (SCI) such that it may be used in the resource allocationprocedure, although it was not agreed how the priority is effectivelyused.

A further topic coming up during discussion was to use the congestionlevel of the channel (i.e., of the PC5 interface) for the resourceallocation procedure, which could be similar to a Channel Busy Rate(CBR) already known from the ETSI standards (see e.g., ETSI EN 302 571v2.0.0 and 102 687 v1.1.1.). Again, no details were discussed in saidrespect, let alone agreements on how to exactly use such a congestionlevel.

As explained above in connection with FIGS. 6 and 7, so as to increasethe reliability of the transmissions, each transport block andscheduling assignment is transmitted over the sidelink with repetitions,i.e., the initial transmission of a scheduling assignment or data isrepeated one or more times. The ongoing discussions in 3GPP have notdistinguished between initial and repeated transmissions of data/SA, andit remains unclear how the semi-persistent scheduling and resourcesensing for V2X transmissions are to be implemented in said respect.

Sensing and semi-persistent scheduling should be implementable in asimple way in order not to increase the complexity of the UE too much.Although general agreements were reached as regards sensing and resourcereservation for V2X transmissions over the PC5 interface, implementingthese mechanisms into current systems might cause problems andinefficiencies.

BRIEF SUMMARY

Non-limiting and exemplary embodiments provide an improved transmissionprocedure for a transmitting device for performing initial transmissionsand retransmissions for data via a sidelink interface. The independentclaims provide non-limiting and exemplary embodiments. Advantageousembodiments are subject to the dependent claims.

According to a first aspect, a transmitting device is provided forperforming initial data transmissions and data retransmissions via thesidelink interface to other devices. It is assumed that a resourcesensing procedure is continuously performed by the transmitting deviceso as to acquire information about future radio resources. According toone example, the radio resource sensing at least comprises monitoringscheduling assignments transmitted by other devices that reserve radioresources at a later point(s) in time, which can then be excluded fromthe radio resource selection. Sensing may optionally also comprisemeasuring the received signal energy in the radio resources. In thefuture, other information might be collected as well during the sensing.

According to the first aspect, one data transmission (e.g., the initialtransmission) is “prioritized” over the remaining (re)transmissions, inthat the vehicular UE performs the resource allocation procedure toselect radio resources for that one data transmission based on theinformation acquired from the radio sensing procedure in a sensingwindow before the data became available for transmission. Consequently,the radio resources selected for this (initial) transmission should notcause a collision with transmissions from other UEs and thus should betransmitted with a high reliability. On the other hand, radio resourcesto be used for the remaining data (re)transmissions are less flexiblyselected so as to be able to reduce the signaling overhead. Inparticular, for the remaining data (re)transmissions, the vehicular UEshall select a suitable data transmission timing pattern (also termed inthe following T-RPT) which defines the timing of one or more datatransmissions, and is used by the vehicular UE with the first datatransmission as a reference to perform the remaining data(re)transmissions. Scheduling information transmitted by the vehicularUE for the data transmission correspondingly indicates the timefrequency resources for the initial transmission as well as the datatransmission timing pattern from which the receiving entities derive thetransmission timing used by the vehicular UE for the first and all theretransmissions. As regards the frequency resources, dataretransmissions performed by the vehicular UE may either use the samefrequencies used for the initial data transmission or use frequenciesderived from the initially used frequencies based on a frequency hoppingpattern; in the latter variant, the scheduling information additionallyshall indicate whether or not hopping is to be used to determine thefrequencies used for the data retransmissions.

According to one variant, the selected data transmission timing patternwill already identify all the transmissions or retransmissions to beperformed for the data. Correspondingly, the (re)transmissions will becompleted within the time period given by the data transmission timingpattern; e.g., within 8 subframes in case of an 8-bit data transmissiontiming pattern.

According to further variants of the first aspect, the selected datatransmission timing pattern will only indicate a single transmission,wherein this one-transmission data transmission timing pattern will berepeated throughout the transmission window after the first datatransmission. By sequentially positioning the selected one-transmissiondata transmission timing pattern, various data retransmission candidatesare defined at those positions of the repeated timing patterns thatindicate the transmission. The vehicular UE will have to select amongthe various data retransmission candidates those candidates that will beindeed used for the retransmission of the data. The selection of theone-transmission T-RPT can be performed by the vehicular UE using theinformation acquired by the resource sensing procedure, such that theresulting data transmission candidates, and particularly the dataretransmission candidates selected later to be actually used, areoptimal from the viewpoint of collision rate and interference.

The selection of the data retransmission candidates may be performedrandomly or may be based on the results of the sensing procedure in saidrespect so as to improve the transmission reliability and to avoidcollisions with transmissions of other UEs. Which of the dataretransmission candidates is actually used by the vehicular UE will thenhave to be indicated to the receiving entities, e.g., as part of thescheduling information transmitted by the vehicular UE for the datatransmission. As regards the frequency resources, the dataretransmissions performed according to the selected data retransmissioncandidates can use either the frequencies already employed by thevehicular UE for the initial data transmission or can follow a frequencyhopping pattern starting from the frequencies used for the initial datatransmission.

According to a further variant of the first aspect, the selection of theone-transmission T-RPT is based on the sensing results of the resourcesensing procedure as follows. The vehicular UE first determines apreferred data retransmission candidate (e.g., the second-highest rankedpossible data retransmission candidate) throughout the transmissionwindow (after the first data transmission), which is then used todetermine the one-transmission T-RPT that, when repeated throughout thetransmission window, has the “1” coincide with that preferred dataretransmission candidate. Consequently, the frequency and time domainresources for the initial transmission as well as for one dataretransmission (i.e., the preferred data transmission candidate) arefreely determined by the vehicular UE based on the sensing results,thereby increasing the reliability of the data transmission and reducingthe collision rate. For this variant, the scheduling information shallnot only indicate the time frequency radio resources for the initialtransmission but also shall separately indicate the frequency resourcesfor this preferred data retransmission. This can be done for instance byproviding a frequency offset with regard to the frequency indicationprovided for the initial data transmission. As before, the T-RPT isindicated in the scheduling assignment so as to provide the transmissiontiming of all the retransmissions, using the initial data transmissionas the reference.

According to a further aspect, radio resources available for thevehicular UE for data transmissions in general, shall be divided intoradio resources to be used for initial data transmissions and radioresources to be used for data retransmissions. Separating the radioresources will make sure that retransmissions and initial transmissionsof data will not collide, thereby protecting the initial transmissionwhich is the most important one.

Correspondingly, in one general first aspect, the techniques disclosedhere feature a transmitting device for transmitting data via a sidelinkinterface to one or more receiving devices. The transmission of the datacomprises a first transmission of the data and, after the first datatransmission, one or more retransmissions of the data. A receiver and aprocessor of the transmitting device perform a resource sensingprocedure so as to acquire information about radio resources usable forthe transmitting device to transmit data at a later point in time. Theprocessor, after data becomes available for transmission, performs anautonomous radio resource allocation to select time-frequency radioresources within a transmission window to be used for performing a firsttransmission of the data, based on the information acquired by theresource sensing procedure during a sensing window before the databecame available for transmission. The processor determines a datatransmission timing pattern among a plurality of data transmissiontiming patterns, each data transmission timing pattern indicating atransmission timing for performing one or more transmissions of data. Atransmitter of the transmitting device performs the first datatransmission using the selected time-frequency radio resources andperforms the one or more data retransmissions at the transmission timingdefined by the determined data transmission timing pattern with respectto the first data transmission.

Correspondingly, in one general first aspect, the techniques disclosedhere feature a method for a transmitting device for transmitting datavia a sidelink interface to one or more receiving devices. Thetransmission of the data comprises a first transmission of the data and,after the first data transmission, one or more retransmissions of thedata. The method comprises the following steps performed by thetransmitting device. A resource sensing procedure is performed so as toacquire information about radio resources usable for the transmittingdevice to transmit data at a later point in time. After data becomesavailable for transmission, an autonomous radio resource allocation isperformed to select time-frequency radio resources within a transmissionwindow to be used for performing a first transmission of the data, basedon the information acquired by the resource sensing procedure during asensing window before the data became available for transmission. Thetransmitting device determines a data transmission timing pattern amonga plurality of data transmission timing patterns, each data transmissiontiming pattern indicating a transmission timing for performing one ormore transmissions of data. The transmitting device performs the firstdata transmission using the selected time-frequency radio resources andperforms the one or more data retransmissions at the transmission timingdefined by the determined data transmission timing pattern with respectto the first data transmission.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and Figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

These general and specific aspects may be implemented using a system, amethod, and a computer program, and any combination of systems, methods,and computer programs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system,

FIG. 2 shows an exemplary downlink resource grid of a downlink slot of asubframe as defined for 3GPP LTE (Release 8/9),

FIG. 3 schematically illustrates how to establish a layer-2 link overthe PC5 for ProSe communication,

FIG. 4 illustrates the use of transmission/reception resources foroverlay (LTE) and underlay (D2D) systems,

FIG. 5 illustrates the transmission of the Scheduling Assignment and theD2D data for two UEs,

FIG. 6 illustrates the D2D communication timing for the UE-autonomousscheduling Mode 2,

FIG. 7 illustrates the D2D communication timing for the eNB-scheduledscheduling Mode 1,

FIG. 8 illustrates an exemplary architecture model for ProSe for anon-roaming scenario,

FIG. 9 illustrates frequency-time radio resources of a data resourcepool for a vehicular UE divided at a time P where data becomes availablefor transmittal, into a transmission window and a sensing window,

FIG. 10 is a sequence diagram for a UE behavior according to anexemplary implementation of the first embodiment,

FIGS. 11 and 12 illustrate a sequence of subframes for a transmissionwindow and the initial data transmission and data retransmissionsaccording to exemplary implementations of the first embodiment,

FIGS. 13 and 14 illustrate a sequence of subframes for a transmissionwindow and the initial data transmission and data retransmissionsaccording to further exemplary implementations of the first embodiment,

FIG. 15 illustrates a sequence of subframes for a transmission windowand the initial data transmission and data retransmissions according toan improved implementation of the first embodiment, and

FIG. 16 illustrates a sequence of subframes for a transmission windowand the initial data transmission and data retransmissions according toa further improved implementation of the first embodiment.

DETAILED DESCRIPTION

A mobile station or mobile node or user terminal or user equipment is aphysical entity within a communication network. One node may haveseveral functional entities. A functional entity refers to a software orhardware module that implements and/or offers a predetermined set offunctions to other functional entities of a node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The term “radio resources” as used in the set of claims and in theapplication is to be broadly understood as referring to physical radioresources, such as time-frequency resources.

The term “direct communication transmission” as used in the applicationis to be broadly understood as a transmission directly between two userequipments, i.e., not via the radio base station (e.g., eNB).Correspondingly, the direct communication transmission is performed overa “direct sidelink connection”, which is the term used for a connectionestablished directly between two user equipments. For example, in 3GPPthe terminology of D2D (Device-to-Device) communication is used or ProSecommunication, or a sidelink communication. The term “direct sidelinkconnection”, “sidelink interface” is to be broadly understood and can beunderstood in the 3GPP context as the PC5 interface described in thebackground section.

The term “ProSe” or in its unabbreviated form, “Proximity Services”,used in the application is applied in the context of Proximity-basedapplications and services in the LTE system as exemplarily explained inthe background section. Other terminology such as “D2D” is also used inthis context to refer to the Device-to-Device communication for theProximity Services.

The term “vehicular mobile terminal” as used throughout the applicationis to be understood in the context of the new 3GPP study itemrespectively work item V2X (vehicular communication) as explained in thebackground section. Correspondingly, a vehicular mobile terminal shallbe broadly understood as a mobile terminal which is specificallyinstalled in a vehicle (e.g., car, commercial trucks, motorcycles etc)to perform vehicular communication, i.e., passing information related tothe vehicle to other entities (such as vehicles, infrastructure,pedestrians) e.g., for the purpose of safety or driver assistance.Optionally, the vehicular mobile terminal may have access to informationavailable at the navigation system (provided it is also installed in thecar), such as map information etc.

The terms “autonomous radio resource allocation” (conversely “radio basestation controlled radio resource allocation”) as used throughout theapplication may exemplarily be understood in the context of 3GPPProximity Services allowing two modes for the resource allocation;namely Mode 1 (i.e., the radio base station controlled radio resourceallocation) according to which the radio base station controls theallocation, and Mode 2 (i.e., autonomous radio resource allocation)according to which the terminal (or transmitting device) autonomouslyselects the resources (without the radio base station).

The term “data transmission timing pattern” as used throughout theapplication may exemplarily be understood as information defining thetiming of transmissions, for instance a T-RPT (time resource pattern oftransmission) as known in the context of 3GPP D2D technology. Dependingon the actual implementation, the data transmission timing pattern maybe used to indicate a first data transmission as well as theretransmissions of the data, or is only used to indicate theretransmissions of the data while the first data transmission isindicated separately.

As explained in the background section, 3GPP has introduced a new studyitem for LTE-assisted vehicular communication, which shall be based onProSe procedures to exchange V2X traffic between the various vehicularmobile terminals and other stations. Furthermore, a kind ofsemi-persistent radio resource allocation shall be supported for V2Xtraffic, and it has been agreed that mechanisms for radio resourcereservation as well as sensing will be supported to said end—inparticular for the UE-autonomous resource allocation mode (also referredto as Mode 2). However, only general agreements have been reached withrespect to sensing and radio resource reservation, without providingdetails on how to implement same and how to adapt other mechanisms so asto ensure efficient and flawless operation. For instance, it remainsunclear how exactly the resource sensing mechanism and radio resourcereservation shall be implemented.

One possible solution will be explained in the following with referenceto FIG. 9, which illustrates in an exemplary and simplified mannerfrequency-time radio resources of a data resource pool of a vehicular UE(transmitting device in general). A PRB pair (Physical Resource Blockpair; 12 subcarriers for one subframe) is taken as unit for exemplarilyillustrating the frequency-time radio resources in the figure. It isassumed that at a time P data becomes available for transmission (i.e.,a packet arrival), and the transmission of the data (as well theretransmissions of the data) should be finished at time L; the timeperiod can be denoted as the transmission window and is dependent on thedelay requirement(s) of the data that is to be transmitted (e.g., 100ms; L=P+100 ms). The results of the sensing procedure obtained within asensing window of e.g., 1000 ms before the packet arrival shall beconsidered for the radio resource allocation procedure to be performedby the vehicular UE to select the frequency-time radio resources (andpossibly other transmission parameters) for transmitting the data. It isexemplarily assumed that three (physical) resource block pairs areneeded for the transmission of the data (further, according to thecurrent standardization, the resource blocks should be contiguous).

One information obtained from the sensing procedure is that particularradio resources in the transmission window are already reserved by otherdevices and should thus not be used by the vehicular UE; thecorresponding boxes for reserved radio resources are striped vertically.The radio resource candidates (each three contiguous resource blockpairs) in the complete transmission window that are available for thevehicular UE to transmit the data are illustrated as framed in FIG. 9.There are six candidates in total in the transmission window, all ofwhich may be ranked according to one or more specific characteristics.As one example, the ranking procedure may rank the various radioresource candidates based on the energy measurements performed duringthe sensing procedure in the sensing window. In more detail, it ispossible to measure the energy (e.g., received signal strength) acrossthe whole sensing window for related radio resource candidates. It isexemplarily assumed that the corresponding radio resource candidates areranked from 1 to 4 as illustrated in FIG. 9 based on the energymeasurements. Correspondingly, radio resource candidates 2, having thesame corresponding frequency radio resources in the sensing window areranked equally. The same applies to the two resource candidates 3. FIG.9 illustrates in diagonal stripes the corresponding radio resources ofthe sensing window, which measured energy is averaged to predict theenergy for radio resource candidates 2. Similarly, FIG. 9 illustratesthe corresponding frequency time radio resources in the sensing windowused for the energy measurement for resource candidate 4 as beingstriped horizontally. Although not illustrated in FIG. 9 for ease ofillustration, corresponding energy measurements and processing areperformed for radio resources in the sensing window corresponding tocandidates 1 and 3 as well.

It is exemplarily assumed that the vehicular UE performs for a singletransport block four transmissions, i.e., a first transmission as wellas three retransmissions. One possible implementation would be to usethe results of the resource sensing procedure for each transmission ofthe data, i.e., for the first as well as for the retransmissions of thedata. In the above presented example of FIG. 9, the vehicular UE couldthus select the four highest-ranked resource candidates for transmittingthe four (re)transmissions. This solution is flexible and efficientlyuses for the transmission of the data (i.e., one transport block) thebest available radio resources in the time domain as well as in thefrequency domain.

However, in order to indicate the radio resources (i.e., time andfrequency within the transmission window) used for each (re)transmissionfor the receiving entities, a scheduling assignment could be transmittedfor each (re)transmission. Alternatively, one scheduling assignmentcould be transmitted which includes all the necessary information forthe receiving entities to be able to receive and properly decode thefirst and all retransmissions. In any case, this significantly increasesthe signaling overhead compared to the prior art solution. In the priorart as exemplified in FIG. 6, one scheduling assignment is transmittedfor all the (re)transmissions, indicating the time-frequency resourcesfor all the transmissions, and indicating the corresponding T-RPTpattern, which uniquely defines the timing of all the (re)transmissions.In the prior art, the frequency resources used for the retransmissionare either the same as used for the first data transmissions (explicitlyindicated in the SA) or follow a frequency hopping pattern starting fromthe frequency resources used for the first data transmission (thescheduling assignment indicates whether a frequency hopping pattern isused or not). If there is no such fixed time and/or frequencyrelationship between the first and the retransmissions, separateinformation on the actually used time-frequency radio resources need tobe provided for each transmission to the receiving entities.

Furthermore, the receiving entities need to be able to associate thefirst and retransmissions of one transport block together, e.g., inorder to enable soft-combining of data. In said respect, a bitmap oflength L-P (100 bits to be able to indicate transmissions within a 100ms transmission window) could be signaled indicating the subframes wherethe transmissions take place, thereby allowing the receiving entities toassociate all transmissions of one transport block together. However,the bitmap would be long and thus would additionally increase thesignaling overhead. Furthermore, the transmission window can havedifferent lengths, and thus the bitmap must be either very long to beable to indicate the longest possible transmission window, or the sizeof the bitmap would change depending on the length of the transmissionwindow, wherein any of the two solutions would be disadvantageous.

The above provides a possible solution to implement the sensingprocedure and the corresponding radio resource allocation for the firsttransmission and retransmissions of the same data, although it involvesseveral disadvantages and problems.

The following exemplary embodiments are conceived by the inventors tomitigate the disadvantage(s) and problem(s) explained above.

Particular implementations of the various embodiments are to beimplemented in the wide specification as given by the 3GPP standards andexplained partly in the background section, with the particular keyfeatures being added as explained in the following embodiments. Itshould be noted that the embodiments may be advantageously used forexample in a mobile communication system, such as 3GPP LTE-A (Release10/11/12/13/14, or later releases) communication systems as described inthe Technical Background section above, but the embodiments are notlimited to its use in these particular exemplary communication networks.

The explanations should not be understood as limiting the scope of thedisclosure, but as mere examples of embodiments to better understand thepresent disclosure. A skilled person should be aware that the generalprinciples of the present disclosure as laid out in the claims can beapplied to different scenarios and in ways that are not explicitlydescribed herein. Several assumptions are made for illustration purposeswhich however shall not restrict the scope of the following embodiments.

The various embodiments mainly focus on improving how a transmittingdevice performs the radio resource allocation and transmission of datavia a sidelink interface, in said respect also suggesting improvementsfor the scheduling assignment content transmitted by the device for thedata transmission. Details will become apparent from the describedembodiments below. Other functionality (i.e., functionality not changedby the various embodiments) may remain exactly the same as explained inthe background section or may be changed without any consequences to thevarious embodiments.

One exemplary scenario to which the various embodiments can be appliedis V2X-communication as exemplified in the background section.Consequently, the transmitting and receiving devices can be e.g., a UEin a vehicle, a road side unit, a “normal” mobile terminal carried by apedestrian etc. Further, the data may be (periodic) vehicular data e.g.,CAM messages, which shall be continuously exchanged among the variousvehicular entities and for which the resource sensing procedure andsemi-persistent resources have been discussed in 3GPP. Although thefollowing exemplary embodiments will be explained for illustrationpurposes in connection with such a V2X-communication scenario, thedisclosure shall not be restricted thereto.

First Embodiment

In the following a first embodiment for solving the above-mentionedproblem(s) will be described in detail. Different implementations andvariants of the first embodiment will be explained as well.

As already mentioned above, exemplarily, a vehicular UE is assumed whichis installed in a vehicle and is capable of performing vehicularcommunication based on the D2D framework as explained in the backgroundsection of this application. Correspondingly, vehicular data (e.g.,periodic and aperiodic data) shall be transmitted by the vehicular UE toother entities for which the data is of interest. It is assumed that theUE supports and mainly performs Mode-2 radio resource allocation and hasbeen properly configured with the necessary resource pool(s) (for dataand scheduling assignments) to be able to autonomously select radioresources for transmitting the scheduling information as well as thedata via the PC5 (sidelink) interface.

The periodic data to be transmitted by the vehicular UE will beexemplified by the Cooperative Awareness Messages (CAMs) explained indetail in the background section. As explained in the backgroundsection, sensing and radio resource reservation have been generallyapproved by 3GPP to be included in future standard release(s) inconnection with the transmission of periodic vehicular data. Inparticular, radio resource reservation at the transmitting side allowsimplementing a kind of “semi-persistent” radio resource allocation, bye.g., reserving the same resources as currently used also for one ormore later time instances to transmit further packets of the periodicdata. Consequently, it is not necessary at those later time instancesfor the vehicular UE to again perform a resource selection/request(Mode-1 or Mode-2 resource allocation) in order to be able to transmitthe periodic data. The radio resource reservation can be implemented indifferent ways and has not been fixed yet by 3GPP. For instance, theradio resource reservation can be done for the next transmissioninstance or for a longer time period (i.e., for more than just the nexttransmission instance of the periodic data). The scheduling information(SCI) transmitted together with sidelink data identifies the radioresources that are used for the transmission and thus allows a receivingentity to properly receive and process/decode the sidelink data. Thescheduling information may additionally be used to indicate the radioresource reservation, e.g., by indicating a time or periodicity of thedata such that the receiving entity can determine for which time (e.g.,subframe) the radio resources are reserved.

The vehicular UE shall further continuously perform the radio sensingprocedure as explained in the background section so as to acquireinformation about future radio resources. This information can then beused during a Mode-2 radio resource allocation procedure performed bythe vehicular UE to select radio resources (and possibly othertransmission parameters) for transmitting the data (optionally thecorresponding scheduling assignment too). The sensing procedure includese.g., decoding the scheduling assignments transmitted by other devicesso as to identify reserved radio resources. Optionally, the sensingprocedure further comprises energy measurements (e.g., the receivedsignal strength, RSSI) throughout the frequency resources for datatransmissions configured for the vehicular UE.

One potential implementation option of the resource sensing procedure isthat every UE has a map with a prediction of frequency resources thatspans over e.g., 100 ms (with e.g., a maximum of 1 second), startingfrom the next subframe. Then, at a time P when a packet arrives at thebuffer in the UE, the UE already has prepared a map of all frequencyresources for subframes P to L (may be termed a transmission window),where L basically corresponds to the maximum time span (according toQoS) until the packet should be transmitted. The frequency map maydistinguish between unavailable and available radio resources (andpossibly also comprises information as to the predicted energy level ofthe different radio resources). Other implementations of the radiosensing procedure are equally possible, e.g., where the UE does notcontinuously update such a future resource map, but rather predicts theradio resources from past measurements in the sensing window only whenneeded.

The transmission of the data includes a first transmission of the data,as well as one or more retransmissions of the data. For instance, it ismainly assumed in the following that the number of total transmissionsis four, or put differently that three retransmissions are performed inaddition to the initial transmission of the data. The number of totaltransmissions for data can be predetermined (e.g., by the standard or anetwork operator) or can be configurable (e.g., by an eNodeB controllingthe vehicular UE, or by the vehicular UE itself). In case the number oftotal transmissions is configurable, the recipients of the data mustsomehow know the number of total transmissions they should expect. Thiscould be ensured for instance by providing corresponding information inthe scheduling assignment or by broadcasting information by the eNodeBin the cell.

One exemplary implementation involves the use of incremental redundancyas already known from 3GPP. In particular, in HARQ operation the eNB cantransmit different coded versions from the original transport block(i.e., the data to be transmitted) in retransmissions so that the UE canemploy incremental-redundancy-(IR)-combining to get additional codinggain via the combining gain. Similarly, it is possible for the V2Xtransmissions over the sidelink interface to use incremental redundancyfor the retransmissions such that different redundancy versions of thesame data are transmitted, e.g., following a predetermined redundancyversion sequence (such as 0, 2, 3, 1, as already defined for the HARQsynchronous non-adaptive retransmission). Consequently, when explainingthat a first transmission and retransmissions of the same data (e.g.,one transport block) is performed, it should not be construed as meaningthat it is exactly the same data but the expression should rather alsocover cases where different redundancy versions of the same data aretransmitted.

In summary, it is assumed that the vehicular UE continuously performs aradio resource sensing procedure to acquire information about futureradio resources (be it reservations and/or RSSI predictions, or otherinformation too). The vehicular UE shall be further able to transmitperiodic (and non-periodic data) and shall in said connection perform aMode-2 resource allocation procedure (UE-autonomous) so as to selectradio resources within a transmission window to be used for thetransmission of the data (may further include the determination of othertransmission parameters such as MCS, etc). The information acquiredthrough the resource sensing procedure shall be used in the resourceallocation procedure so as to improve same.

Different variants of the first embodiment will be explained in thefollowing. The first embodiment provides an improved transmissionprocedure for the data transmissions to be performed via the PC5sidelink interface. The first embodiment prioritizes one of the datatransmissions (e.g., the initial data transmission) by fully using theradio resource sensing results for the resource allocation to improvethe reliability of the initial transmission. On the other hand, theresource allocation is less flexible for the remaining data(re)transmissions which thus will not benefit from the resource sensingprocedure in the same manner as the initial transmission but whichallows reducing the signaling overhead. When using incrementalredundancy, the first transmission is the most important one, since itis the first transmission received by the receiving entity and since itis self decodable which might not be the case for other redundancyversions.

When data becomes available for transmission, the vehicular UE shallperform the UE-autonomous radio resource allocation procedure in orderto obtain the necessary transmission parameters, including the selectionof time-frequency radio resources within the transmission window so asto perform a first transmission of the pending data. The resourceallocation procedure shall take the results obtained by the sensingprocedure during a sensing window before the data arrival (see sensingwindow in FIG. 9) fully into account when determining the radioresources to be used for the initial transmission of the data. Forinstance, reserved radio resources should be avoided, and a best radioresource candidate can be selected among various candidates that areranked based on energy measurements performed during the sensing window.

In order to also determine how to perform the retransmissions of thedata, the transmitting device shall determine a suitable datatransmission timing pattern (such as the T-RPT known from the backgroundsection) which defines a timing pattern of one or more datatransmissions. The T-RPT is usually a bitmap having a length of severalbits (e.g., 8 bits), each bit being associated with a possibletransmission timing (e.g., one subframe) of the data. A plurality ofT-RPTs can be defined. For instance, the T-RPTs can have differentnumber of transmissions, where an 8-bit T-RPT can indicate up from 1 to8 transmissions. Furthermore, the positions of the transmission(s) canvary in a T-RPT, where there can be e.g., 8 different T-RPTs indicatinga single transmission. How many and which T-RPTs are defined in thetransmitting device can be predetermined (e.g., by a standard or networkoperator) or may be configurable (e.g., by the eNodeB controlling thevehicular UE). According to one example, the T-RPTs already defined forthe D2D communication for 3GPP Releases 12 and 13 can be reused. In anycase, the vehicular UE shall select a suitable T-RPT so as to determinethe timing at which the retransmissions of the data will be performed.The T-RPT, and thus the data transmission(s) indicated thereby, is thuspositioned in the transmission window using the first transmission as areference. For instance, the selected T-RPT may be immediately followingthe first data transmission, or may include the first data transmissionas part of the T-RPT.

Correspondingly, the vehicular UE will perform the first datatransmission according to the selected time-frequency radio resources,and then performs the data retransmissions at the transmission timingsdefined by the selected T-RPT. Furthermore, the retransmissionsperformed by the vehicular UE can either be using the same frequencies(i.e., PRBs) as already used for the initial transmission, or can usefrequencies derived from the frequencies of the initial transmissionbased on a frequency hopping pattern (as e.g., known from the priorart).

The first embodiment thus provides a solution combining an improvedfirst data transmission which is based on the sensing results, while atthe same time using simple transmission patterns to coordinate the dataretransmissions with the first transmission as a reference.Correspondingly, the information to be provided to the receivingentities is thus rather limited, and does not cause a high signalingoverhead. In particular, the scheduling assignment transmitted by thevehicular UE for the data transmission indicates the time-frequencyradio resources for the first transmission as well as the selectedT-RPT, such that the receiving entities are able to receive the firstdata transmission as well as the data retransmissions. Optionally, thescheduling assignment may further include information as to whether afrequency hopping pattern was used for the frequency resources used forthe data retransmissions.

FIG. 10 is a sequence diagram for a UE behavior according to anexemplary implementation of the first embodiment, in line with the aboveexplanations. As apparent therefrom, the resource sensing procedure isillustrated separately from the sequence of steps to be performed by theUE to transmit data that is pending for transmission. Using dashedlines, FIG. 10 illustrates how information provided by the resourcesensing procedure, such as the radio resource reservations or the energypredictions made during the sensing window, can be used as input invarious steps of the procedure. For instance, the UE-autonomous radioresource allocation can exclude reserved radio resources from theselection, so as to avoid interference. Also, the selection of theappropriate T-RPT can also be based on the information acquired by thesensing procedure, as will be explained in more detail in connectionwith further implementations of the embodiment.

A first detailed implementation of the general first embodimentdiscussed above will be explained in connection with FIGS. 11 and 12,which both illustrate a sequence of subframes of a transmission windowand the corresponding timing of data transmissions, including an initialtransmission and three retransmissions of data. In the exemplaryillustration, the transmission window is depicted so as to includesubframe P at which the data becomes available as well as subframe Lwhich is considered the latest subframe while still complying with thedelay requirement of the data. The transmission window can also bedefined differently, e.g., not including subframe 10 or even furthersubsequent subframes 11, . . . , in order to take a processing time intoaccount.

In both figures it is assumed that the vehicular UE determinestime-frequency radio resources in subframe 12 to be optimal for thefirst data transmission. The corresponding indication would be includedin the corresponding scheduling assignment such that the receivingentities are able to receive the data. As assumed so far, fourtransmissions are to be performed in total for data (e.g., one transportblock) so as to increase the transmission reliability. In thisimplementation, the vehicular UE would thus select the T-RPT accordingto the total number of transmissions that are to be performed. There aretwo variants depicted in FIGS. 11 and 12, distinguishing whether or notthe T-RPT includes or does not include the initial data transmission. Inthe variant illustrated in FIG. 11, the vehicular UE would thus selectthe T-RPT among T-RPTs having four total transmissions; an exemplaryT-RPT that could be selected by the vehicular UE is shown in FIG. 11. Onthe other hand, in the variant illustrated in FIG. 12, the vehicular UEwould thus select the T-RPT among T-RPTs having three transmissions intotal in view of that the first transmission is not comprised by theT-RPT.

The T-RPT in the variant of FIG. 12 exemplarily starts immediately afterthe subframe in which the initial transmission is performed.Alternatively, while still using subframe 12 (i.e., the timing of thefirst data transmission) as a reference for the start of the T-RPT (andthus the retransmission timings), a different timing offset from thefirst data transmission timing could be used. For instance, the T-RPTmay start at a distance of one or more subframes from the first datatransmission. The timing offset may be either configurable (e.g., by thevehicular UE or the eNodeB) or predetermined, but needs to be known tothe receiving entities.

Furthermore, the retransmissions performed at the various subframes(subframes 14, 15, and 19 in the variant of FIG. 11, or subframes 15,16, and 20 in the variant of FIG. 12), can use either the samefrequencies as already used for the first data transmission or can use“hopped” frequencies derived from the frequencies used for the firstdata transmission (based on a known frequency hopping pattern).

As mentioned above, the selection of the T-RPT is restricted by thenumber of total transmissions (see FIG. 11) or number of retransmissions(see FIG. 12). Apart from this restriction, in one exemplary variant,the vehicular UE may randomly determine the T-RPT (having the necessarynumber of (re)transmissions) among all those T-RPTs having saidnecessary number of (re)transmissions. Although this would be a simpleimplementation, this may have the disadvantage that the randomly chosentiming pattern can result in retransmission timings (subframes) thatwould cause severe interference with transmissions of other devices; asnoted above, the frequency resources are fixed by the frequencyresources selected for the initial data transmission, either being thesame frequency resources or following a frequency hopping patterntherefrom.

Alternatively, instead of randomly determining the T-RPT, the vehicularUE can take the results of the sensing procedure into account as far aspossible. In particular, the same physical resource blocks that arereserved in one subframe can be available in another subframe, such thatthe vehicular UE shall—as much as possible—reduce the interference withtransmissions from other UEs by appropriately selecting the T-RPT basedon the sensed information.

Similarly, whether or not to use hopping for the frequency domainresources can also be based on the results of the sensing procedure,such that the vehicular UE chooses to use hopping or not hopping for thefrequency domain depending on which frequency resources e.g., wouldpresumably cause the least interference.

The determination of the timing pattern as well as whether or not to usefrequency hopping are interrelated since different frequencies atdifferent subframes will lead to different collisions and interference.Correspondingly, the appropriate T-RPT as well as whether or not to usefrequency hopping can be determined together so as to combine thebenefits of selecting an optimal T-RPT and optimal PRBs.

As already mentioned above, the scheduling assignment transmitted forthe whole data transmission needs to indicate the time-frequencyresources for the initial data transmission as well as the selectedT-RPT, which is the main information for the receiving entities toderive the timing of the first as well as of the remainingretransmissions of the data. Optionally, the scheduling assignment mayfurther include information on whether frequency hopping is used or notwith regard to the frequencies used for the initial transmission.Correspondingly, the scheduling assignment is compact and does not causea high signaling overhead.

The retransmission of the data will thus be completed within the timeperiod given by the determined T-RPT, in this exemplary case within 7(see FIG. 11) or 8 (see FIG. 12) subframes. In other words, theretransmissions must be performed within a time window which isrelatively short, especially compared to the exemplary delay requirementof 100 ms. This reduces the flexibility of the vehicular UE to transmitthe retransmissions. Although one variant also takes into account thesensing results. The probability of collisions with data transmissionsby other UEs can still be high and may be hardly avoided, due to thevery limited flexibility of the discussed variants as there are only afew different T-RPTs within a very short time frame.

Further implementations of the first embodiment are provided in thefollowing so as to improve the above discussed variants of the firstembodiment. As will be explained in connection with FIGS. 13 and 14,instead of restricting the retransmissions to a particular timeframegiven by the length of the timing pattern (as in FIGS. 11 and 12),another exemplary implementation of the first embodiment extends theretransmission possibilities throughout the whole remaining transmissionwindow. In particular, in the same manner as explained above inconnection with FIGS. 11 and 12, the vehicular UE shall perform theradio resource allocation for determining optimal radio resources forthe first transmission of the data, based on the information obtained bythe resource sensing procedure. In the present example it is assumedthat the vehicular UE determines optimal time-frequency radio resourcesin subframe 14, such that the initial transmission is performed in thosedetermined frequencies of subframe 14.

On the other hand, a data transmission timing pattern is selected by thevehicular UE that comprises only one transmission, i.e., only onetransmission for the whole T-RPT. This one-transmission T-RPT is howeverthen repeated throughout the remaining transmission window after thefirst transmission and having the first data transmission timing as areference so as to thus define several data retransmission candidates.For instance, as illustrated in FIG. 14, the repeated T-RPTs can startat the next subframe after the first data transmission timing (othertiming offsets from the first data transmission timing are possible aswell, as discussed above in connection with FIG. 12). Alternatively, asillustrated in FIG. 13, the repeated T-RPTs start such that the first ofthe repeated T-RPTs (more precisely the “1” in that first T-RPT bitmap)coincides with the first data transmission timing.

By thus positioning the repeated T-RPTs after the first datatransmission timing, each T-RPT defines one data retransmissioncandidate, namely at those subframes where the repeated T-RPT indicatesthe one transmission. The data retransmission candidates are thusdistributed throughout the remaining transmission window (e.g., afterthe first data transmission timing) and are equally spaced from oneanother in accordance with a length of the T-RPT. For instance, in theexemplary implementation given in FIG. 13, the first data transmissionis defined to occur in subframe 14, such that the data retransmissioncandidates would be in subframes 22, 30, 38, 46 . . . 110 (each having adistance in between of 8 subframes, coinciding with the length of theT-RPT).

Given the assumption that the transmission window is 100 ms and thetransmission pattern is 8 bits, there can be a maximum of in between 12(e.g., for FIG. 14) and up to 14 (e.g., for FIG. 13) different dataretransmission candidates (also depending on the actual implementationused). The last T-RPT can be truncated and thus may or may not yieldanother data retransmission opportunity depending on the position of the“1” data transmission within the (truncated) T-RPT.

The vehicular UE then can select data retransmission candidates, amongthe thus defined data retransmission candidates, to be indeed used forthe data retransmissions. The determination of course again depends onthe number of total transmissions (i.e., number of totalretransmissions). In the exemplary scenario assumed for FIG. 13, it isassumed that only two total transmissions are to be performed, i.e.,only one retransmission is needed, such that only one out of theavailable data retransmission candidates has to be selected by thevehicular UE. In the exemplary scenario illustrated in FIG. 13, it isassumed that the vehicular UE decides to transmit the single dataretransmission at subframe 30, which is associated with the third of thesequence of T-RPTs. In the exemplary scenario illustrated in FIG. 14, itis assumed that three total data transmissions are to be performed bythe vehicular UE, and thus two retransmission candidates have to beselected by the vehicular UE; assumed to be in subframes 22 and 38,i.e., again the first and third of the repeated T-RPTs.

In order for the receiving entities to know where the vehicular UE willperform the first transmission and the retransmission(s), the schedulingassignment shall not only indicate the time-frequency radio resourcesfor the first transmission and the selected T-RPT (as already discussedbefore), but also information on the data retransmission candidates thevehicular UE will actually use for data (re)transmission. One possibleoption on how to indicate the used data retransmission candidates amongall candidates is to provide a bitmap (e.g., called T-RPT selectionbitmap) in the scheduling assignment, wherein the bits of the T-RPTselection bitmap are associated with the repeated T-RPTs therebyuniquely identifying one of the repeated T-RPTs. As illustrated in FIGS.13 and 14, the T-RPT selection bitmap can be of different lengthdepending on the implementation and should have a length so as to beable to flexibly indicate all data retransmission candidates. Asapparent from the figures, the “1” in the T-RPT selection bitmap pointsto that T-RPT the vehicular UE actually used for performing theretransmission. The T-RPT selection bitmap is to be included in thescheduling assignment, which although slightly increasing the signalingoverhead provides the benefit of greatly increasing the flexibility forperforming the retransmissions.

In order to improve the retransmission reliability and reduce possiblecollisions with other data transmissions, the vehicular UE may determinethe one-transmission T-RPT as well as the data retransmission candidatesto be actually used for the retransmissions based on the resultsobtained from the sensing procedure. In particular, there are at most 8different one-transmission T-RPTs (assuming 8-bit T-RPTs) each of whichwould respectively define different data retransmission candidatesthroughout the transmission window. Furthermore, among the thus defineddata retransmission candidates (for instance 13 candidates), there areseveral different combination of candidates to perform the dataretransmissions. Overall, depending on the one-transmission T-RPT andthe resulting options to perform the data retransmissions, the vehicularUE shall select that combination of T-RPT and data retransmissioncandidate(s) that would yield e.g., the least interference according tothe predictions obtained from the sensing procedure.

Moreover, the vehicular UE may either use the same frequencies as usedfor the initial data transmission, or it may use frequencies derivedfrom the frequencies of the first data transmission based on a hoppingpattern. As explained before, also this decision can be based on theresults of the sensing procedure, e.g., taking into account that radioresource reservations may be different from one PRB to the other withina single subframe. Consequently, there can be three different levels offreedom available for the vehicular UE so as to optimize the dataretransmission reliability; i.e., the one-transmission T-RPT, theactually-used retransmission candidates among all the retransmissioncandidates, and the frequency resources being based on hopping or not.The three freedom levels are interrelated and can be chosen togetherbased on the sensing results obtained before during the sensing windowso as to benefit as much as possible from the sensing results whileallowing a simple (re)transmission procedure.

According to another implementation, the solution as presented anddiscussed in connection with FIGS. 13 and 14 is further improved byselecting one of the data retransmission resources based on the sensingresults as follows. In particular, FIG. 15 illustrates a sequence ofsubframes of a transmission window available for a UE to transmit data,and is similar to FIG. 14 discussed above. In the same manner as for thesolution presented in connection with FIGS. 13 and 14, the vehicular UEshall perform the radio resource allocation procedure for determiningoptimal radio resources for the first data transmission, based oninformation obtained by the resource sensing procedure. Further, aone-transmission T-RPT is to be selected by the vehicular UE, which isrepeatedly positioned throughout the remaining transmission window withthe first data transmission as a reference. Differently than theprevious solutions, in order to determine the T-RPT, the vehicular UEfirst shall determine an optimal retransmission candidate within theremaining transmission window (i.e., after the first data transmission),based on the sensing results. Based on the sensing results, thevehicular UE can freely select the frequency and time resources for thispreferred retransmission candidate such that collision withtransmissions by other UEs can be avoided.

The time position of this selected preferred retransmission candidatethen is used by the vehicular UE for determining the T-RPT. This will beexplained in connection with FIG. 15. It is exemplarily assumed that apreferred retransmission candidate is found in subframe 26 (e.g., it isthe second-highest-ranked candidate, whereas the highest-rankedcandidate is selected by the UE to be used for the first transmission ofdata). Exemplarily assuming that the positioning of the repeated T-RPTsof length 8 bit starts immediately after the first data transmission(see FIG. 15), the vehicular UE would thus select the T-RPT 00010000,such that one of the “1” of the repeated T-RPTs coincides with thepreferred data retransmission candidate selected before (see subframe26). Correspondingly, one of the data retransmissions performed by thevehicular UE shall take place at subframe 26 on the frequencies asselected during the resource allocation procedure based on the sensingresults (i.e., the used frequencies at subframe 26 can be different fromthose frequencies used for the initial data transmission in subframe14). Exemplarily, in FIG. 15 it is assumed that the first dataretransmission is performed at the preferred data retransmissioncandidate, while a further retransmission is performed at the nextretransmission possibility at subframe 34. The T-RPT selection bitmapalready mentioned before, would have to indicate these retransmissions,and thus indicates the second and third T-RPT as being used by thevehicular UE for the data retransmissions.

As already explained in the preceding implementation, the vehicle UE mayhave to select further data retransmission candidates among theremaining data retransmission candidates. This may be done for instanceby using the results of the sensing procedure so as to avoid collisionswith transmissions of other UEs.

This improved solution of FIG. 15 produces a reduced collision rate andthus increases the transmission reliability of the data by additionallyselecting the time and frequency resources for one of the dataretransmissions freely based on the sensing results obtained earlier.However, this solution increases the signaling overhead slightly. Asalready discussed before for the implementation according to FIGS. 13and 14, the scheduling assignment transmitted by the vehicular UE forthe data indicates the time-frequency radio resources for the first datatransmission as well as the selected T-RPT and the T-RPT selectionbitmap. While the T-RPT in combination with the T-RPT selection bitmapand taking the first data transmission timing as a reference, uniquelyidentify the timing of all of the remaining data retransmissions, thereceiving entities need to know about the frequencies that are used bythe vehicular UE to transmit the data retransmission at the preferredradio resources (see e.g., subframe 26 above) since the frequencies arefreely selected based on the sensing results and thus will not coincidewith the frequencies already indicated in the scheduling assignment forthe first data transmission (or do not comply with a frequency hoppingpattern). One solution is thus to include information on the otherfrequencies used for this one retransmission at subframe 26; this can bedone by explicitly identifying the frequencies or by including afrequency offset from the frequencies used for the first datatransmission. The frequency offset may be used by the receiving entitiesto determine the frequencies used for that one data retransmission atsubframe 26.

Moreover, the same frequencies as used for the first or the onepreferred data retransmission can also be used for transmitting theremaining data retransmissions. Alternatively, a hopping frequencypattern with regard to the frequencies used for the first datatransmission or the preferred data retransmission can be used for theremaining data retransmissions. A corresponding frequency hoppingindication in the scheduling assignment appropriately informs thereceiving entities in said respect.

A further improvement for the radio resource allocation performed for aninitial data transmission and data retransmissions will be explained inthe following. According to an exemplary implementation, the dataresource pool, which comprises a plurality of time-frequency radioresources as illustrated in a simplified manner in FIG. 9, is dividedinto time-frequency radio resources that are only available forperforming first data transmissions while the remaining time-frequencyradio resources in the data resource pool are only available forperforming data retransmissions. Alternatively, two different dataresource pools can be provided, one data resource pool for initial datatransmissions and the other data resource pool for data retransmissions.In any case, during the resource allocation procedure, the vehicular UEuses different resources for an initial transmission and a dataretransmission. The data resource pool segregation shall apply e.g., toall vehicular UEs in a corresponding cell. Therefore, by segregating theavailable resources for data transmissions between initial datatransmissions and data retransmissions, it is possible to protect theinitial transmission even further, since collisions with retransmissionsare theoretically not possible.

The segregation of the available time-frequency resources can be done invarious manners. For instance, a corresponding formula can be providedwhich is then used by the vehicular UE as well as by other UEs todetermine which time-frequency radio resources are to be used forinitial data transmissions and which are to be used for dataretransmissions. A simple formula can e.g., be based on the modulooperation. Further, the different data resource pools for initial datatransmissions and data retransmissions can be configured by the eNodeB,by appropriately broadcasting system information.

In one particular exemplary variant, the segregation is performed in thetime domain such that subframes are either used for initialtransmissions or retransmissions.

This improvement can be e.g., applied to the implementation discussed inconnection with FIG. 9 where the vehicle UE performs a radio resourceallocation procedure for each (re)transmission. Further, the improvementcan also be applied to the implementation as discussed above inconnection with FIG. 11-15. For instance, with regard to the solutionspresented in FIGS. 11 and 12, a further improved solution would performthe radio resource selection for the first transmission amongtime-frequency resources available for the initial transmission only.Then, the selected T-RPT pattern (selected randomly or based on thesensing results) would indicate only subframes that are indeed availablein the data resource pool directed to data retransmissions. FIG. 16exemplarily illustrates an implementation where subframes that are notavailable for the retransmissions are crossed out. For instance, it isassumed that only every third subframe is available for aretransmission, in particular subframes 14, 17, 20, 23, 26, 29 etc. Asapparent, the bits of the T-RPT bitmap correspondingly indicate onlysubframes that are indeed available for retransmissions (with theexception of the first bit of the T-RPT in this variant, which isassumed to indicate the first transmission). As a result, using the sameT-RPT bitmap as in the exemplary scenario used for FIG. 11 (10110001),the vehicular UE would perform the retransmissions at subframes 17, 20,and 32.

Similarly, for the implementations according to FIGS. 13, 14 and 15, therepeated T-RPT patterns would be repeated throughout subframes of thetransmission window belonging to the retransmission-restricted dataresource pool. As regards the solution in FIG. 15, the radio resourceallocation performed exclusively for the one preferred dataretransmission (in subframe 26) would select resources within theretransmission-restricted data resource pool.

Further Embodiments

According to a first aspect, a transmitting device is provided fortransmitting data via a sidelink interface to one or more receivingdevices. The transmission of the data comprises a first transmission ofthe data and, after the first data transmission, one or moreretransmissions of the data. A receiver and a processor of thetransmitting device perform a resource sensing procedure so as toacquire information about radio resources usable for the transmittingdevice to transmit data at a later point in time. The processor, afterdata becomes available for transmission, performs an autonomous radioresource allocation to select time-frequency radio resources within atransmission window to be used for performing a first transmission ofthe data, based on the information acquired by the resource sensingprocedure during a sensing window before the data became available fortransmission. The processor determines a data transmission timingpattern among a plurality of data transmission timing patterns, eachdata transmission timing pattern indicating a transmission timing forperforming one or more transmissions of data. A transmitter of thetransmitting device performs the first data transmission using theselected time-frequency radio resources and performs the one or moredata retransmissions at the transmission timing defined by thedetermined data transmission timing pattern with respect to the firstdata transmission.

According to a second aspect which is provided in addition to the firstaspect, the plurality of data transmission timing patterns indicates adifferent number of data transmissions. The processor determines onedata transmission timing pattern among data transmission timing patternscorresponding to a total number of transmissions to be performed for thedata; in one optional implementation, the total number of transmissionsto be performed for the data is determined by the processor or ispreconfigured. According to one option, the one or more dataretransmissions are performed within a time span defined by the lengthof the one determined data transmission timing pattern. The datatransmission timing pattern is determined by the processor eitherrandomly or based on the information acquired by the resource sensingprocedure during the sensing window.

According to a third aspect which is provided in addition to one of thefirst to second aspects, the transmitter transmits a schedulingassignment indicating the selected time-frequency radio resources forthe first data transmission and identifying the determined datatransmission timing pattern.

According to a fourth aspect in addition to the first aspect, thedetermined data transmission timing pattern indicates only one datatransmission. The processor determines data retransmission candidateswithin the transmission window for performing the one or more dataretransmissions by repeating the determined data transmission timingpattern a plurality of times within the transmission window with respectto the timing of the first data transmission and by then identifying thetiming position given by the one indicated data transmission perrepeated data transmission timing pattern. The processor determineswhich data retransmission candidates are to be used for performing theone or more data retransmissions, which may be optionally done dependingon a total number of transmissions to be performed for the data, wherethe total number of data transmissions can be determined by theprocessor or be preconfigured, According to an option, the processordetermines the data transmission timing pattern as well as the dataretransmission candidates to be used for the data retransmission basedon the information acquired by the resource sensing procedure during thesensing window.

According to a fifth aspect in addition to one of the first to fourthaspects, the one or more data retransmissions are performed using thesame frequency radio resources as used for the first data transmissionor using frequency radio resources determined by the processor from thefrequency radio resources used for the first data transmission based ona frequency hopping pattern. According to an option, the processordetermines for the one or more data retransmissions whether to use thesame frequency radio resources as for the first data transmission or touse frequency radio resources following the frequency hopping pattern,based on the information acquired by the resource sensing procedureduring the sensing window. According to further option, the schedulingassignment further indicates whether or not a frequency hopping patternis used by the transmitting device for determining frequency radioresources used for transmitting the one or more data retransmissions.

According to a sixth aspect in addition to the first aspect, thedetermined data transmission timing pattern indicates only onetransmission. The processor determines a preferred transmission timing,after the first data transmission timing, for one of the one or moredata retransmission based on the information acquired by the resourcesensing procedure during the sensing window. The processor determinesthe data transmission timing pattern such that the one indicated datatransmission of the data transmission timing pattern coincides with thedetermined preferred transmission timing when the data transmissiontiming pattern is repeated a plurality of times within the transmissionwindow with respect to the timing of the first data transmission. Dataretransmission candidates are defined within the transmission window forperforming one or more of the data retransmissions, by repeating thedata transmission timing pattern and by then identifying the timingposition given by the one indicated data transmission per repeated datatransmission timing pattern. The processor determines which dataretransmission candidates are to be used for performing remaining dataretransmissions, which can be optionally done based on the informationacquired by the resource sensing procedure during the sensing window anddepending on a total number of transmissions to be performed for thedata. The total number of data transmissions can be determined by theprocessor or be preconfigured, The transmitter transmits one dataretransmission at the determined preferred transmission timing, andtransmits the remaining data retransmissions at the retransmissioncandidates determined to be used.

According to the seventh aspect in addition to the sixth aspect, ascheduling assignment transmitted by the transmitter indicates thefrequency radio resources for the data retransmission at the preferredtransmission timing. For instance, the indication of the frequencyresources for the data retransmission at the preferred transmissiontiming can be an offset with respect to the frequency radio resourcesfor the first data transmission. According to an option, the remainingdata retransmissions are performed using the same frequency radioresources as used for the first data transmission or the same frequencyradio resources as used for the data retransmission at the preferredtransmission timing. Alternatively, the remaining data retransmissionsare performed using frequency radio resources determined by theprocessor based on a frequency hopping pattern from the frequency radioresources used for the first data transmission or from the frequencyradio resources used for the data retransmission at the preferredtransmission timing. Correspondingly, the scheduling assignment furtherindicates whether or not a frequency hopping pattern is used by thetransmitting device for determining frequency radio resources used fortransmitting the one or more data retransmissions.

According to eighth aspect in addition to one of the fourth to seventhaspects, the transmitter transmits a scheduling assignment indicatingthe selected time-frequency radio resources for the first datatransmission and identifying the determined data transmission timingpattern. The scheduling assignment further indicates which datatransmission timing pattern among the plurality of repeated datatransmission timing patterns define the transmitting timing forperforming the one or more data retransmissions. Optionally, the datatransmitting timing pattern indication is encoded as a bitmap, whereinbits of the bitmap are respectively associated with one of the pluralityof repeated data transmission timing patterns.

According to ninth aspect in addition to one of the first to eighthaspects, the data transmission timing pattern has a length of aplurality of bits. Each bit of the data transmission timing patternindicates whether or not a transmission of the data is to be performedat a transmission timing associated with the respective bit position.Optionally, the data transmission timing pattern is positioned in thetiming window with respect to the first data transmission so as to alsoindicate or not indicate the first data transmission.

According to tenth aspect in addition to one of the first to ninthaspects, a data resource pool comprises a plurality of time-frequencyradio resources available for the transmitting device to perform datatransmissions. The data resource pool is divided into time-frequencyradio resources available for performing first data transmissions andinto time-frequency radio resources available for performing dataretransmissions. Then, the processor selects, during the autonomousradio resource allocation, time-frequency radio resources to be used forperforming the first data transmission among the time-frequency radioresources available for performing first data transmissions. Optionally,the plurality of time-frequency radio resources of the data resourcepool is divided in the time domain between time-frequency radioresources for first data transmissions and for data retransmissions. Asa further option, the division of the data resource pool ispreconfigured or configured by a radio base station controlling thetransmitting device.

According to eleventh aspect in addition to one of the seventh to tenthaspects, the resource sensing procedure comprises:

-   -   in order to determine radio resources that are reserved by other        transmitting devices, the receiver and processor, when in        operation, monitor for scheduling assignments transmitted by        other transmitting devices indicating radio resources reserved        by the other transmitting devices for a later point in time, and    -   optionally measures a received signal energy in radio resources        so as to identify radio resources that are used by other        transmitting devices for transmission,

As an option, the autonomous radio resource allocation comprisesexcluding the radio resources reserved by other transmitting devicesfrom the plurality of transmission radio resources.

According to a twelfth aspect, a method is provided for a transmittingdevice for transmitting data via a sidelink interface to one or morereceiving devices. The transmission of the data comprises a firsttransmission of the data and, after the first data transmission, one ormore retransmissions of the data. The method comprises the followingsteps performed by the transmitting device. A resource sensing procedureis performed so as to acquire information about radio resources usablefor the transmitting device to transmit data at a later point in time.After data becomes available for transmission, an autonomous radioresource allocation is performed to select time-frequency radioresources within a transmission window to be used for performing a firsttransmission of the data, based on the information acquired by theresource sensing procedure during a sensing window before the databecame available for transmission. The transmitting device determines adata transmission timing pattern among a plurality of data transmissiontiming patterns, each data transmission timing pattern indicating atransmission timing for performing one or more transmissions of data.The transmitting device perform the first data transmission using theselected time-frequency radio resources and performs the one or moredata retransmissions at the transmission timing defined by thedetermined data transmission timing pattern with respect to the firstdata transmission.

According to a thirteenth aspect provided in addition to the twelfthaspect, the plurality of data transmission timing patterns indicates adifferent number of data transmissions. The method comprises determiningone data transmission timing pattern among data transmission timingpatterns corresponding to a total number of transmissions to beperformed for the data. Optionally, the total number of transmissions tobe performed for the data is determined by the transmitting device or ispreconfigured. Optionally, the one or more data retransmissions areperformed within a time span defined by the length of the one determineddata transmission timing pattern. Optionally, the data transmissiontiming pattern is determined by the transmitting device either randomlyor based on the information acquired by the resource sensing procedureduring the sensing window.

According to a fourteenth aspect provided in addition to the twelfth orthirteenth aspect, the method further comprises the step of transmittinga scheduling assignment that indicates the selected time-frequency radioresources for the first data transmission and identifies the determineddata transmission timing pattern.

According to a fifteenth aspect provided in addition to the twelfthaspect, the determined data transmission timing pattern indicates onlyone data transmission. The method comprises the step of determining dataretransmission candidates within the transmission window for performingthe one or more data retransmissions by repeating the determined datatransmission timing pattern a plurality of times within the transmissionwindow with respect to the timing of the first data transmission and bythen identifying the timing position given by the one indicated datatransmission per repeated data transmission timing pattern. The methodcomprises the step of determining which data retransmission candidatesare to be used for performing the one or more data retransmissions,which may optionally depend on a total number of transmissions to beperformed for the data, where the total number of data transmissionsbeing determined by the processor or being preconfigured. Optionally,the method comprises the step of determining the data transmissiontiming pattern as well as the data retransmission candidates to be usedfor the data retransmission based on the information acquired by theresource sensing procedure during the sensing window.

According to a sixteenth aspect provided in addition to one of thetwelfth to fifteenth aspects, the one or more data retransmissions areperformed using the same frequency radio resources as used for the firstdata transmission or using frequency radio resources determined from thefrequency radio resources used for the first data transmission based ona frequency hopping pattern. Optionally, the method comprises the stepof determining for the one or more data retransmissions whether to usethe same frequency radio resources as for the first data transmission orto use frequency radio resources following the frequency hoppingpattern, based on the information acquired by the resource sensingprocedure during the sensing window. Optionally, the schedulingassignment further indicates whether or not a frequency hopping patternis used by the transmitting device for determining frequency radioresources used for transmitting the one or more data retransmissions.

According to a seventeenth aspect provided in addition to the twelfthaspects, the determined data transmission timing pattern indicates onlyone transmission. The method comprises the step of determining apreferred transmission timing, after the first data transmission timing,for one of the one or more data retransmission based on the informationacquired by the resource sensing procedure during the sensing window.The method comprises the step of determining the data transmissiontiming pattern such that the one indicated data transmission of the datatransmission timing pattern coincides with the determined preferredtransmission timing when the data transmission timing pattern isrepeated a plurality of times within the transmission window withrespect to the timing of the first data transmission. Dataretransmission candidates are defined within the transmission window forperforming one or more of the data retransmissions, by repeating thedata transmission timing pattern and by then identifying the timingposition given by the one indicated data transmission per repeated datatransmission timing pattern. The method comprises the step ofdetermining which data retransmission candidates are to be used forperforming remaining data retransmissions, which may be optionally basedon the information acquired by the resource sensing procedure during thesensing window and depending on a total number of transmissions to beperformed for the data, where the total number of data transmissionsbeing determined by the transmitting device or being preconfigured. Themethod comprises the step of transmitting one data retransmission at thedetermined preferred transmission timing, and transmitting the remainingdata retransmissions at the retransmission candidates determined to beused.

According to an eighteenth aspect in addition to the seventeenth aspect,a scheduling assignment transmitted by the transmitter indicates thefrequency radio resources for the data retransmission at the preferredtransmission timing, optionally as an offset with respect to thefrequency radio resources for the first data transmission. Optionally,the remaining data retransmissions are performed using the samefrequency radio resources as used for the first data transmission or thesame frequency radio resources as used for the data retransmission atthe preferred transmission timing. Alternatively, the remaining dataretransmissions are performed using frequency radio resources determinedby the processor based on a frequency hopping pattern from the frequencyradio resources used for the first data transmission or from thefrequency radio resources used for the data retransmission at thepreferred transmission timing. The scheduling assignment furtherindicates whether or not a frequency hopping pattern is used by thetransmitting device for determining frequency radio resources used fortransmitting the one or more data retransmissions.

According to a nineteenth aspect provided in addition to one of thefifteenth to the eighteenth aspects, wherein the method furthercomprises the step of transmitting a scheduling assignment indicatingthe selected time-frequency radio resources for the first datatransmission and identifying the determined data transmission timingpattern. The scheduling assignment further indicates which datatransmission timing pattern among the plurality of repeated datatransmission timing patterns define the transmitting timing forperforming the one or more data retransmissions. Optionally, the datatransmitting timing pattern indication is encoded as a bitmap, whereinbits of the bitmap are respectively associated with one of the pluralityof repeated data transmission timing patterns.

According to a twentieth aspect provided in addition to one of thetwelfth to nineteenth aspects, the data transmission timing pattern hasa length of a plurality of bits, and each bit of the data transmissiontiming pattern indicates whether or not a transmission of the data is tobe performed at a transmission timing associated with the respective bitposition. Optionally, the data transmission timing pattern is positionedin the timing window with respect to the first data transmission so asto also indicate or not indicate the first data transmission.

According to a twenty-first aspect provided in addition to one of thetwelfth to twentieth aspects, a data resource pool comprises a pluralityof time-frequency radio resources available for the transmitting deviceto perform data transmissions. The data resource pool is divided intotime-frequency radio resources available for performing first datatransmissions and into time-frequency radio resources available forperforming data retransmissions. The method comprises the step ofselecting, during the autonomous radio resource allocation,time-frequency radio resources to be used for performing the first datatransmission among the time-frequency radio resources available forperforming first data transmissions. Optionally, the plurality oftime-frequency radio resources of the data resource pool is divided inthe time domain between time-frequency radio resources for first datatransmissions and for data retransmissions. Optionally, the division ofthe data resource pool is preconfigured or configured by a radio basestation controlling the transmitting device.

Hardware and Software Implementation of the Present Disclosure

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware, software, or software incooperation with hardware. In this connection a user terminal (mobileterminal) is provided. The user terminal is adapted to perform themethods described herein, including corresponding entities toparticipate appropriately in the methods, such as receiver, transmitter,processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. The various embodiments may also be performed or embodied by acombination of these devices. In particular, each functional block usedin the description of each embodiment described above can be realized byan LSI as an integrated circuit. They may be individually formed aschips, or one chip may be formed so as to include a part or all of thefunctional blocks. They may include a data input and output coupledthereto. The LSI here may be referred to as an IC, a system LSI, a superLSI, or an ultra LSI depending on a difference in the degree ofintegration. However, the technique of implementing an integratedcircuit is not limited to the LSI and may be realized by using adedicated circuit or a general-purpose processor. In addition, a FPGA(Field Programmable Gate Array) that can be programmed after themanufacture of the LSI or a reconfigurable processor in which theconnections and the settings of circuits cells disposed inside the LSIcan be reconfigured may be used.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It shouldbe further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A transmitting device for transmitting data via a sidelink interfaceto one or more receiving devices, wherein the transmission of the datacomprises a first transmission of the data and, after the first datatransmission, one or more retransmissions of the data, the transmittingdevice comprising: a receiver and a processor, which in operation,perform a resource sensing procedure so as to acquire information aboutradio resources usable for the transmitting device to transmit data at alater point in time, the processor, which in operation and after databecomes available for transmission, performs an autonomous radioresource allocation to select time-frequency radio resources within atransmission window to be used for performing a first transmission ofthe data, based on the information acquired by the resource sensingprocedure during a sensing window before the data became available fortransmission, and the processor, which in operation, determines a datatransmission timing pattern among a plurality of data transmissiontiming patterns, each data transmission timing pattern indicating atransmission timing for performing one or more transmissions of data, atransmitter, which in operation, performs the first data transmissionusing the selected time-frequency radio resources and performs the oneor more data retransmissions at the transmission timing defined by thedetermined data transmission timing pattern with respect to the firstdata transmission.
 2. The transmitting device according to claim 1,wherein the plurality of data transmission timing patterns indicates adifferent number of data transmissions, and the processor, when inoperation, determines one data transmission timing pattern among datatransmission timing patterns corresponding to a total number oftransmissions to be performed for the data, wherein the total number oftransmissions to be performed for the data is determined by theprocessor or is preconfigured, wherein the one or more dataretransmissions are performed within a time span defined by the lengthof the one determined data transmission timing pattern, wherein the datatransmission timing pattern is determined by the processor eitherrandomly or based on the information acquired by the resource sensingprocedure during the sensing window.
 3. The transmitting deviceaccording to claim 1, wherein the transmitter, when in operation,transmits a scheduling assignment indicating the selected time-frequencyradio resources for the first data transmission and identifying thedetermined data transmission timing pattern.
 4. The transmitting deviceaccording to claim 1, wherein the determined data transmission timingpattern indicates only one data transmission, wherein the processor,when in operation, determines data retransmission candidates within thetransmission window for performing the one or more data retransmissionsby repeating the determined data transmission timing pattern a pluralityof times within the transmission window with respect to the timing ofthe first data transmission and by then identifying the timing positiongiven by the one indicated data transmission per repeated datatransmission timing pattern, and wherein the processor, when inoperation, determines which data retransmission candidates are to beused for performing the one or more data retransmissions, depending on atotal number of transmissions to be performed for the data, the totalnumber of data transmissions being determined by the processor or beingpreconfigured, wherein the processor, when in operation, determines thedata transmission timing pattern as well as the data retransmissioncandidates to be used for the data retransmission based on theinformation acquired by the resource sensing procedure during thesensing window.
 5. The transmitting device according to claim 1, towherein the one or more data retransmissions are performed using thesame frequency radio resources as used for the first data transmissionor using frequency radio resources determined by the processor from thefrequency radio resources used for the first data transmission based ona frequency hopping pattern, wherein the processor, when in operation,determines for the one or more data retransmissions whether to use thesame frequency radio resources as for the first data transmission or touse frequency radio resources following the frequency hopping pattern,based on the information acquired by the resource sensing procedureduring the sensing window, wherein the scheduling assignment furtherindicates whether or not a frequency hopping pattern is used by thetransmitting device for determining frequency radio resources used fortransmitting the one or more data retransmissions.
 6. The transmittingdevice according to claim 1, wherein the determined data transmissiontiming pattern indicates only one transmission, wherein the processor,when in operation, determines a preferred transmission timing, after thefirst data transmission timing, for one of the one or more dataretransmission based on the information acquired by the resource sensingprocedure during the sensing window, and wherein the processor, when inoperation, determines the data transmission timing pattern such that theone indicated data transmission of the data transmission timing patterncoincides with the determined preferred transmission timing when thedata transmission timing pattern is repeated a plurality of times withinthe transmission window with respect to the timing of the first datatransmission, wherein data retransmission candidates are defined withinthe transmission window for performing one or more of the dataretransmissions, by repeating the data transmission timing pattern andby then identifying the timing position given by the one indicated datatransmission per repeated data transmission timing pattern, and theprocessor, when in operation, determines which data retransmissioncandidates are to be used for performing remaining data retransmissions,based on the information acquired by the resource sensing procedureduring the sensing window and depending on a total number oftransmissions to be performed for the data, the total number of datatransmissions being determined by the processor or being preconfigured,wherein the transmitter, when in operation, transmits one dataretransmission at the determined preferred transmission timing, andtransmits the remaining data retransmissions at the retransmissioncandidates determined to be used.
 7. The transmitting device accordingto claim 6, wherein a scheduling assignment transmitted by thetransmitter indicates the frequency radio resources for the dataretransmission at the preferred transmission timing, as an offset withrespect to the frequency radio resources for the first datatransmission, and wherein the remaining data retransmissions areperformed using the same frequency radio resources as used for the firstdata transmission or the same frequency radio resources as used for thedata retransmission at the preferred transmission timing, or wherein theremaining data retransmissions are performed using frequency radioresources determined by the processor based on a frequency hoppingpattern from the frequency radio resources used for the first datatransmission or from the frequency radio resources used for the dataretransmission at the preferred transmission timing, and wherein thescheduling assignment further indicates whether or not a frequencyhopping pattern is used by the transmitting device for determiningfrequency radio resources used for transmitting the one or more dataretransmissions.
 8. The transmitting device according to claim 4,wherein the transmitter, when in operation, transmits a schedulingassignment indicating the selected time-frequency radio resources forthe first data transmission and identifying the determined datatransmission timing pattern, wherein the scheduling assignment furtherindicates which data transmission timing pattern among the plurality ofrepeated data transmission timing patterns define the transmittingtiming for performing the one or more data retransmissions, wherein thedata transmitting timing pattern indication is encoded as a bitmap,wherein bits of the bitmap are respectively associated with one of theplurality of repeated data transmission timing patterns.
 9. Thetransmitting device according to claim 1, wherein the data transmissiontiming pattern has a length of a plurality of bits, and each bit of thedata transmission timing pattern indicates whether or not a transmissionof the data is to be performed at a transmission timing associated withthe respective bit position, and wherein the data transmission timingpattern is positioned in the timing window with respect to the firstdata transmission so as to also indicate or not indicate the first datatransmission.
 10. The transmitting device according to claim 1, whereina data resource pool comprises a plurality of time-frequency radioresources available for the transmitting device to perform datatransmissions, the data resource pool being divided into time-frequencyradio resources available for performing first data transmissions andinto time-frequency radio resources available for performing dataretransmissions, and wherein the processor, when in operation, selects,during the autonomous radio resource allocation, time-frequency radioresources to be used for performing the first data transmission amongthe time-frequency radio resources available for performing first datatransmissions, wherein the plurality of time-frequency radio resourcesof the data resource pool is divided in the time domain betweentime-frequency radio resources for first data transmissions and for dataretransmissions, wherein the division of the data resource pool ispreconfigured or configured by a radio base station controlling thetransmitting device.
 11. The transmitting device according to claim 1,wherein the resource sensing procedure comprises: in order to determineradio resources that are reserved by other transmitting devices, thereceiver and processor, when in operation, monitor for schedulingassignments transmitted by other transmitting devices indicating radioresources reserved by the other transmitting devices for a later pointin time, and measures a received signal energy in radio resources so asto identify radio resources that are used by other transmitting devicesfor transmission, wherein the autonomous radio resource allocationcomprises excluding the radio resources reserved by other transmittingdevices from the plurality of transmission radio resources.
 12. A methodfor a transmitting device for transmitting data via a sidelink interfaceto one or more receiving devices, wherein the transmission of the datacomprises a first transmission of the data and, after the first datatransmission, one or more retransmissions of the data, the methodcomprising the following steps performed by the transmitting device:performing a resource sensing procedure so as to acquire informationabout radio resources usable for the transmitting device to transmitdata at a later point in time, after data becomes available fortransmission, performing an autonomous radio resource allocation toselect time-frequency radio resources within a transmission window to beused for performing a first transmission of the data, based on theinformation acquired by the resource sensing procedure during a sensingwindow before the data became available for transmission, anddetermining a data transmission timing pattern among a plurality of datatransmission timing patterns, each data transmission timing patternindicating a transmission timing for performing one or moretransmissions of data, performing the first data transmission using theselected time-frequency radio resources and performing the one or moredata retransmissions at the transmission timing defined by thedetermined data transmission timing pattern with respect to the firstdata transmission.
 13. The method according to claim 12, wherein theplurality of data transmission timing patterns indicates a differentnumber of data transmissions, and the method comprises determining onedata transmission timing pattern among data transmission timing patternscorresponding to a total number of transmissions to be performed for thedata, wherein the total number of transmissions to be performed for thedata is determined by the transmitting device or is preconfigured,wherein the one or more data retransmissions are performed within a timespan defined by the length of the one determined data transmissiontiming pattern, wherein the data transmission timing pattern isdetermined by the transmitting device either randomly or based on theinformation acquired by the resource sensing procedure during thesensing window.
 14. The method according to claim 12, further comprisingthe step of: transmitting a scheduling assignment that indicates theselected time-frequency radio resources for the first data transmissionand identifies the determined data transmission timing pattern.
 15. Themethod according to claim 12, wherein the determined data transmissiontiming pattern indicates only one data transmission, and the methodcomprises the steps of: determining data retransmission candidateswithin the transmission window for performing the one or more dataretransmissions by repeating the determined data transmission timingpattern a plurality of times within the transmission window with respectto the timing of the first data transmission and by then identifying thetiming position given by the one indicated data transmission perrepeated data transmission timing pattern, and determining which dataretransmission candidates are to be used for performing the one or moredata retransmissions, depending on a total number of transmissions to beperformed for the data, the total number of data transmissions beingdetermined by the processor or being preconfigured, wherein the methodcomprises the step of determining the data transmission timing patternas well as the data retransmission candidates to be used for the dataretransmission based on the information acquired by the resource sensingprocedure during the sensing window.
 16. The method according to claim12, wherein the one or more data retransmissions are performed using thesame frequency radio resources as used for the first data transmissionor using frequency radio resources determined from the frequency radioresources used for the first data transmission based on a frequencyhopping pattern, wherein the method comprises the step of determiningfor the one or more data retransmissions whether to use the samefrequency radio resources as for the first data transmission or to usefrequency radio resources following the frequency hopping pattern, basedon the information acquired by the resource sensing procedure during thesensing window, wherein the scheduling assignment further indicateswhether or not a frequency hopping pattern is used by the transmittingdevice for determining frequency radio resources used for transmittingthe one or more data retransmissions.
 17. The method according to claim12, wherein the determined data transmission timing pattern indicatesonly one transmission, wherein the method comprises the steps of:determining a preferred transmission timing, after the first datatransmission timing, for one of the one or more data retransmissionbased on the information acquired by the resource sensing procedureduring the sensing window, and determining the data transmission timingpattern such that the one indicated data transmission of the datatransmission timing pattern coincides with the determined preferredtransmission timing when the data transmission timing pattern isrepeated a plurality of times within the transmission window withrespect to the timing of the first data transmission, wherein dataretransmission candidates are defined within the transmission window forperforming one or more of the data retransmissions, by repeating thedata transmission timing pattern and by then identifying the timingposition given by the one indicated data transmission per repeated datatransmission timing pattern, determining which data retransmissioncandidates are to be used for performing remaining data retransmissions,based on the information acquired by the resource sensing procedureduring the sensing window and depending on a total number oftransmissions to be performed for the data, the total number of datatransmissions being determined by the transmitting device or beingpreconfigured, and transmitting one data retransmission at thedetermined preferred transmission timing, and transmitting the remainingdata retransmissions at the retransmission candidates determined to beused.
 18. The method according to claim 17, wherein a schedulingassignment transmitted by the transmitter indicates the frequency radioresources for the data retransmission at the preferred transmissiontiming, as an offset with respect to the frequency radio resources forthe first data transmission, and wherein the remaining dataretransmissions are performed using the same frequency radio resourcesas used for the first data transmission or the same frequency radioresources as used for the data retransmission at the preferredtransmission timing, or wherein the remaining data retransmissions areperformed using frequency radio resources determined by the processorbased on a frequency hopping pattern from the frequency radio resourcesused for the first data transmission or from the frequency radioresources used for the data retransmission at the preferred transmissiontiming, and wherein the scheduling assignment further indicates whetheror not a frequency hopping pattern is used by the transmitting devicefor determining frequency radio resources used for transmitting the oneor more data retransmissions.
 19. The method according to claim 15,further comprising the step of transmitting a scheduling assignmentindicating the selected time-frequency radio resources for the firstdata transmission and identifying the determined data transmissiontiming pattern, wherein the scheduling assignment further indicateswhich data transmission timing pattern among the plurality of repeateddata transmission timing patterns define the transmitting timing forperforming the one or more data retransmissions, wherein the datatransmitting timing pattern indication is encoded as a bitmap, whereinbits of the bitmap are respectively associated with one of the pluralityof repeated data transmission timing patterns.
 20. The method accordingto claim 12, wherein the data transmission timing pattern has a lengthof a plurality of bits, and each bit of the data transmission timingpattern indicates whether or not a transmission of the data is to beperformed at a transmission timing associated with the respective bitposition, and wherein the data transmission timing pattern is positionedin the timing window with respect to the first data transmission so asto also indicate or not indicate the first data transmission. 21.(canceled)